diff --git a/m4/ccflags.m4 b/m4/ccflags.m4
index 49cfdac..f634d09 100644
--- a/m4/ccflags.m4
+++ b/m4/ccflags.m4
@@ -85,10 +85,17 @@ AC_CACHE_VAL([local_cv_prog_cc_error_flag],
 	AC_MSG_CHECKING([if ${CC} supports an error flag])
 	AC_LANG_PUSH([C])
 	save_CFLAGS="${CFLAGS}"
-	CFLAGS="${CFLAGS} -Werror"
-	AC_TRY_LINK([], [],
-		[local_cv_prog_cc_error_flag=-Werror],
-		[local_cv_prog_cc_error_flag=no])
+	local_cv_prog_cc_error_flag="-Werror" # GCC
+	CFLAGS="${save_CFLAGS} ${local_cv_prog_cc_error_flag}"
+	AC_TRY_LINK([], [], [],
+	[
+	  local_cv_prog_cc_error_flag="-errwarn" # Sun C
+	  CFLAGS="${save_CFLAGS} ${local_cv_prog_cc_error_flag}"
+	  AC_TRY_LINK([], [], [],
+	  [
+	    local_cv_prog_cc_error_flag=no]
+	  )]
+	)
 	CFLAGS="${save_CFLAGS}"
 	AC_LANG_POP([C])
 	if test x"${local_cv_prog_cc_error_flag}" != "xno"; then
diff --git a/m4/libshout.m4 b/m4/libshout.m4
index 5cd4371..90c8583 100644
--- a/m4/libshout.m4
+++ b/m4/libshout.m4
@@ -1,9 +1,9 @@
 dnl # $Id$
 
 dnl # Check for a working installation of libshout.
-dnl # Provides appropriate --with configuration options, fills and substitutes
-dnl # the LIBSHOUT_CFLAGS, LIBSHOUT_CPPFLAGS, LIBSHOUT_LDFLAGS and
-dnl # LIBSHOUT_LIBS variables accordingly.
+dnl # Provides appropriate --with configuration options, fills the
+dnl # LIBSHOUT_CFLAGS, LIBSHOUT_CPPFLAGS, LIBSHOUT_LDFLAGS and LIBSHOUT_LIBS
+dnl # variables accordingly.
 
 
 dnl # Copyright (c) 2009 Moritz Grimm <mgrimm@mrsserver.net>
@@ -39,11 +39,6 @@ AC_ARG_VAR([LIBSHOUT_CPPFLAGS],
 	[C preprocessor flags for libshout])
 AC_ARG_VAR([LIBSHOUT_LDFLAGS],
 	[linker flags for libshout])
-if test x"${prefix}" = "xNONE"; then
-	have_libshout_prefix="/usr/local"
-else
-	have_libshout_prefix="${prefix}"
-fi
 have_libshout_includes=""
 have_libshout_libs=""
 want_libshout="auto"
@@ -92,30 +87,29 @@ esac
 AC_CACHE_VAL([local_cv_have_lib_libshout_opts],
 [
 ax_check_libshout_shout_pc="no"
-PKG_CONFIG_PATH="${PKG_CONFIG_PATH}:${have_libshout_prefix}/lib/pkgconfig"
 PKG_CHECK_EXISTS([shout], [ax_check_libshout_shout_pc=yes])
 if test -z "${LIBSHOUT_CFLAGS}" \
     -a x"${ax_check_libshout_shout_pc}" = "xyes"; then
 	LIBSHOUT_CFLAGS="`${PKG_CONFIG} --cflags-only-other shout`"
 fi
 if test -n "${LIBSHOUT_CPPFLAGS}"; then
-	if test x"${have_libshout_includes}" != "x"; then
+	if test -n "${have_libshout_includes}"; then
 		LIBSHOUT_CPPFLAGS="${LIBSHOUT_CPPFLAGS} -I${have_libshout_includes}"
 	fi
 else
-	if test x"${have_libshout_includes}" != "x"; then
+	if test -n "${have_libshout_includes}"; then
 		LIBSHOUT_CPPFLAGS="-I${have_libshout_includes}"
 	else
 		if test x"${want_libshout}" = "xauto" \
 		    -a x"${ax_check_libshout_shout_pc}" = "xyes"; then
 			LIBSHOUT_CPPFLAGS="`${PKG_CONFIG} --cflags-only-I shout`"
-		else
+		elif test -n "${have_libshout_prefix}"; then
 			LIBSHOUT_CPPFLAGS="-I${have_libshout_prefix}/include"
 		fi
 	fi
 fi
 if test -n "${LIBSHOUT_LDFLAGS}"; then
-	if test x"${have_libshout_libs}" != "x"; then
+	if test -n "${have_libshout_libs}"; then
 		LIBSHOUT_LDFLAGS="-L${have_libshout_libs} ${LIBSHOUT_LDFLAGS}"
 	fi
 else
@@ -128,7 +122,7 @@ else
 				`${PKG_CONFIG} --libs-only-L shout` \
 				`${PKG_CONFIG} --libs-only-other shout` \
 			"
-		else
+		elif test -n "${have_libshout_prefix}"; then
 			LIBSHOUT_LDFLAGS="-L${have_libshout_prefix}/lib"
 		fi
 	fi
@@ -150,7 +144,6 @@ local_cv_have_lib_libshout=no
 
 if test x"${want_libshout}" != "xno"; then	# want_libshout != no
 
-PKG_CONFIG_PATH="${PKG_CONFIG_PATH}:${have__libshout_prefix}/lib/pkgconfig"
 if test -z "${PKG_CONFIG}"; then
 	AC_MSG_ERROR([The pkg-config utility is required.], [1])
 fi
diff --git a/m4/libvorbis.m4 b/m4/libvorbis.m4
index b2ff634..75f01e0 100644
--- a/m4/libvorbis.m4
+++ b/m4/libvorbis.m4
@@ -2,8 +2,8 @@ dnl $Id$
 
 dnl # Check for working installations of libvorbis, libvorbisfile and
 dnl # libvorbisenc.
-dnl # Provides appropriate --with configuration options, fills and substitutes
-dnl # the VORBIS_CFLAGS, VORBIS_CPPFLAGS, VORBIS_LDFLAGS, LIBVORBIS_LIBS,
+dnl # Provides appropriate --with configuration options, fills the
+dnl # VORBIS_CFLAGS, VORBIS_CPPFLAGS, VORBIS_LDFLAGS, LIBVORBIS_LIBS,
 dnl # LIBVORBISENC_LIBS and LIBVORBISFILE_LIBS variables accordingly.
 
 
@@ -50,11 +50,6 @@ AC_ARG_VAR([VORBIS_CPPFLAGS],
 	[C preprocessor flags for the Vorbis libraries])
 AC_ARG_VAR([VORBIS_LDFLAGS],
 	[linker flags for the Vorbis libraries])
-if test x"${prefix}" = "xNONE"; then
-	have_libvorbis_prefix="/usr/local"
-else
-	have_libvorbis_prefix="${prefix}"
-fi
 have_libvorbis_includes=""
 have_libvorbis_libs=""
 want_libvorbis="auto"
@@ -103,30 +98,29 @@ esac
 AC_CACHE_VAL([local_cv_have_lib_libvorbis_opts],
 [
 ax_check_libvorbis_vorbis_pc="no"
-PKG_CONFIG_PATH="${PKG_CONFIG_PATH}:${have_libvorbis_prefix}/lib/pkgconfig"
 PKG_CHECK_EXISTS([vorbis], [ax_check_libvorbis_vorbis_pc=yes])
 if test -z "${VORBIS_CFLAGS}" \
     -a x"${ax_check_libvorbis_vorbis_pc}" = "xyes"; then
 	VORBIS_CFLAGS="`${PKG_CONFIG} --cflags-only-other vorbis`"
 fi
 if test -n "${VORBIS_CPPFLAGS}"; then
-	if test x"${have_libvorbis_includes}" != "x"; then
+	if test -n "${have_libvorbis_includes}"; then
 		VORBIS_CPPFLAGS="${VORBIS_CPPFLAGS} -I${have_libvorbis_includes}"
 	fi
 else
-	if test x"${have_libvorbis_includes}" != "x"; then
+	if test -n "${have_libvorbis_includes}"; then
 		VORBIS_CPPFLAGS="-I${have_libvorbis_includes}"
 	else
 		if test x"${want_libvorbis}" = "xauto" \
 		    -a x"${ax_check_libvorbis_vorbis_pc}" = "xyes"; then
 			VORBIS_CPPFLAGS="`${PKG_CONFIG} --cflags-only-I vorbis`"
-		else
+		elif test -n "${have_libvorbis_prefix}"; then
 			VORBIS_CPPFLAGS="-I${have_libvorbis_prefix}/include"
 		fi
 	fi
 fi
 if test -n "${VORBIS_LDFLAGS}"; then
-	if test x"${have_libvorbis_libs}" != "x"; then
+	if test -n "${have_libvorbis_libs}"; then
 		VORBIS_LDFLAGS="-L${have_libvorbis_libs} ${VORBIS_LDFLAGS}"
 	fi
 else
@@ -139,7 +133,7 @@ else
 				`${PKG_CONFIG} --libs-only-L vorbis` \
 				`${PKG_CONFIG} --libs-only-other vorbis` \
 			"
-		else
+		elif test -n "${have_libvorbis_prefix}"; then
 			VORBIS_LDFLAGS="-L${have_libvorbis_prefix}/lib"
 		fi
 	fi
@@ -160,7 +154,6 @@ local_cv_have_lib_libvorbis=no
 
 if test x"${want_libvorbis}" != "xno"; then	# want_libvorbis != no
 
-PKG_CONFIG_PATH="${PKG_CONFIG_PATH}:${have_libvorbis_prefix}/lib/pkgconfig"
 if test -z "${PKG_CONFIG}"; then
 	AC_MSG_ERROR([The pkg-config utility is required.], [1])
 fi
@@ -255,7 +248,6 @@ local_cv_have_lib_libvorbisfile=no
 
 if test x"${want_libvorbis}" != "xno"; then	# want_libvorbis != no
 
-PKG_CONFIG_PATH="${PKG_CONFIG_PATH}:${have_libvorbis_prefix}/lib/pkgconfig"
 if test -z "${PKG_CONFIG}"; then
 	AC_MSG_ERROR([The pkg-config utility is required.], [1])
 fi
@@ -339,7 +331,6 @@ local_cv_have_lib_libvorbisenc=no
 
 if test x"${want_libvorbis}" != "xno"; then	# want_libvorbis != no
 
-PKG_CONFIG_PATH="${PKG_CONFIG_PATH}:${have_libvorbis_prefix}/lib/pkgconfig"
 if test -z "${PKG_CONFIG}"; then
 	AC_MSG_ERROR([The pkg-config utility is required.], [1])
 fi
diff --git a/m4/libxml2.m4 b/m4/libxml2.m4
index b31ea90..6c27428 100644
--- a/m4/libxml2.m4
+++ b/m4/libxml2.m4
@@ -1,8 +1,8 @@
 dnl # $Id$
 
 dnl # Check for a working installation of libxml (version 2.)
-dnl # Provides appropriate --with configuration options, fills and substitutes
-dnl # the LIBXML2_CFLAGS, LIBXML2_CPPFLAGS, LIBXML2_LDFLAGS and LIBXML2_LIBS
+dnl # Provides appropriate --with configuration options, fills the
+dnl # LIBXML2_CFLAGS, LIBXML2_CPPFLAGS, LIBXML2_LDFLAGS and LIBXML2_LIBS
 dnl # variables accordingly.
 
 
@@ -38,11 +38,6 @@ AC_ARG_VAR([LIBXML2_CPPFLAGS],
 	[C preprocessor flags for libxml2])
 AC_ARG_VAR([LIBXML2_LDFLAGS],
 	[linker flags for libxml2])
-if test x"${prefix}" = "xNONE"; then
-	have_libxml2_prefix="/usr/local"
-else
-	have_libxml2_prefix="${prefix}"
-fi
 have_libxml2_includes=""
 have_libxml2_libs=""
 want_libxml2="auto"
@@ -91,30 +86,29 @@ esac
 AC_CACHE_VAL([local_cv_have_lib_libxml2_opts],
 [
 ax_check_libxml2_xml2_pc="no"
-PKG_CONFIG_PATH="${PKG_CONFIG_PATH}:${have_libxml2_prefix}/lib/pkgconfig"
 PKG_CHECK_EXISTS([libxml-2.0], [ax_check_libxml2_xml2_pc=yes])
 if test -z "${LIBXML2_CFLAGS}" \
     -a x"${ax_check_libxml2_xml2_pc}" = "xyes"; then
 	LIBXML2_CFLAGS="`${PKG_CONFIG} --cflags-only-other libxml-2.0`"
 fi
 if test -n "${LIBXML2_CPPFLAGS}"; then
-	if test x"${have_libxml2_includes}" != "x"; then
+	if test -n "${have_libxml2_includes}"; then
 		LIBXML2_CPPFLAGS="${LIBXML2_CPPFLAGS} -I${have_libxml2_includes}"
 	fi
 else
-	if test x"${have_libxml2_includes}" != "x"; then
+	if test -n "${have_libxml2_includes}"; then
 		LIBXML2_CPPFLAGS="-I${have_libxml2_includes}"
 	else
 		if test x"${want_libxml2}" = "xauto" \
 		    -a x"${ax_check_libxml2_xml2_pc}" = "xyes"; then
 			LIBXML2_CPPFLAGS="`${PKG_CONFIG} --cflags-only-I libxml-2.0`"
-		else
+		elif test -n "${have_libxml2_prefix}"; then
 			LIBXML2_CPPFLAGS="-I${have_libxml2_prefix}/include"
 		fi
 	fi
 fi
 if test -n "${LIBXML2_LDFLAGS}"; then
-	if test x"${have_libxml2_libs}" != "x"; then
+	if test -n "${have_libxml2_libs}"; then
 		LIBXML2_LDFLAGS="-L${have_libxml2_libs} ${LIBXML2_LDFLAGS}"
 	fi
 else
@@ -127,7 +121,7 @@ else
 				`${PKG_CONFIG} --libs-only-L libxml-2.0` \
 				`${PKG_CONFIG} --libs-only-other libxml-2.0` \
 			"
-		else
+		elif test -n "${have_libxml2_prefix}"; then
 			LIBXML2_LDFLAGS="-L${have_libxml2_prefix}/lib"
 		fi
 	fi
@@ -148,7 +142,6 @@ local_cv_have_lib_libxml2=no
 
 if test x"${want_libxml2}" != "xno"; then	# want_libxml2 != no
 
-PKG_CONFIG_PATH="${PKG_CONFIG_PATH}:${have_libxml2_prefix}/lib/pkgconfig"
 if test -z "${PKG_CONFIG}"; then
 	AC_MSG_ERROR([The pkg-config utility is required.], [1])
 fi
@@ -172,7 +165,7 @@ CFLAGS="${CFLAGS} ${LIBXML2_CFLAGS}"
 CPPFLAGS="${CPPFLAGS} ${LIBXML2_CPPFLAGS}"
 LDFLAGS="${LDFLAGS} ${LIBXML2_LDFLAGS}"
 LIBS="${LIBXML2_LIBS} ${LIBS}"
-AC_CHECK_HEADERS([libxml/parser.h],
+AC_CHECK_HEADER([libxml/parser.h],
 [
 	AC_MSG_CHECKING([if libxml2 works])
 	AC_LINK_IFELSE(
diff --git a/m4/taglib.m4 b/m4/taglib.m4
index bd1acb1..8cf7dda 100644
--- a/m4/taglib.m4
+++ b/m4/taglib.m4
@@ -2,8 +2,8 @@ dnl # $Id$
 
 dnl # Check for working installations of TagLib and its C-wrapper library,
 dnl # libtag_c.
-dnl # Provides appropriate --with configuration options, fills and substitutes
-dnl # the TAGLIB_CFLAGS, TAGLIB_CPPFLAGS, TAGLIB_LDFLAGS, TAGLIB_LIBS and
+dnl # Provides appropriate --with configuration options, fills the
+dnl # TAGLIB_CFLAGS, TAGLIB_CPPFLAGS, TAGLIB_LDFLAGS, TAGLIB_LIBS and
 dnl # TAGLIB_C_LIBS variables accordingly.
 
 
@@ -45,11 +45,6 @@ AC_ARG_VAR([TAGLIB_CPPFLAGS],
 	[C preprocessor flags for TagLib])
 AC_ARG_VAR([TAGLIB_LDFLAGS],
 	[linker flags for TagLib])
-if test x"${prefix}" = "xNONE"; then
-	have_taglib_prefix="/usr/local"
-else
-	have_taglib_prefix="${prefix}"
-fi
 have_taglib_includes=""
 have_taglib_libs=""
 want_taglib="auto"
@@ -98,30 +93,29 @@ esac
 AC_CACHE_VAL([local_cv_have_lib_taglib_opts],
 [
 ax_check_taglib_taglib_pc="no"
-PKG_CONFIG_PATH="${PKG_CONFIG_PATH}:${have_taglib_prefix}/lib/pkgconfig"
 PKG_CHECK_EXISTS([taglib], [ax_check_taglib_taglib_pc=yes])
 if test -z "${TAGLIB_CFLAGS}" \
     -a x"${ax_check_taglib_taglib_pc}" = "xyes"; then
 	TAGLIB_CFLAGS="`${PKG_CONFIG} --cflags-only-other taglib`"
 fi
 if test -n "${TAGLIB_CPPFLAGS}"; then
-	if test x"${have_taglib_includes}" != "x"; then
+	if test -n "${have_taglib_includes}"; then
 		TAGLIB_CPPFLAGS="${TAGLIB_CPPFLAGS} -I${have_taglib_includes}"
 	fi
 else
-	if test x"${have_taglib_includes}" != "x"; then
+	if test -n "${have_taglib_includes}"; then
 		TAGLIB_CPPFLAGS="-I${have_taglib_includes}"
 	else
 		if test x"${want_taglib}" = "xauto" \
 		    -a x"${ax_check_taglib_taglib_pc}" = "xyes"; then
 			TAGLIB_CPPFLAGS="`${PKG_CONFIG} --cflags-only-I taglib`"
-		else
+		elif test -n "${have_taglib_prefix}"; then
 			TAGLIB_CPPFLAGS="-I${have_taglib_prefix}/include/taglib"
 		fi
 	fi
 fi
 if test -n "${TAGLIB_LDFLAGS}"; then
-	if test x"${have_taglib_libs}" != "x"; then
+	if test -n "${have_taglib_libs}"; then
 		TAGLIB_LDFLAGS="-L${have_taglib_libs} ${TAGLIB_LDFLAGS}"
 	fi
 else
@@ -134,7 +128,7 @@ else
 				`${PKG_CONFIG} --libs-only-L taglib` \
 				`${PKG_CONFIG} --libs-only-other taglib` \
 			"
-		else
+		elif test -n "${have_taglib_prefix}"; then
 			TAGLIB_LDFLAGS="-L${have_taglib_prefix}/lib"
 		fi
 	fi
@@ -155,7 +149,6 @@ local_cv_have_lib_taglib=no
 
 if test x"${want_taglib}" != "xno"; then	# want_taglib != no
 
-PKG_CONFIG_PATH="${PKG_CONFIG_PATH}:${have_taglib_prefix}/lib/pkgconfig"
 if test -z "${PKG_CONFIG}"; then
 	AC_MSG_ERROR([The pkg-config utility is required.], [1])
 fi
@@ -260,7 +253,6 @@ local_cv_have_lib_taglib_c=no
 
 if test x"${want_taglib}" != "xno"; then	# want_taglib != no
 
-PKG_CONFIG_PATH="${PKG_CONFIG_PATH}:${have_taglib_prefix}/lib/pkgconfig"
 if test -z "${PKG_CONFIG}"; then
 	AC_MSG_ERROR([The pkg-config utility is required.], [1])
 fi