Mist configure.in fixes and simplifications

- Remove AC_PROG_MAKE_SET; we's be using GNU.
 - Don't AC_SUBST() SPARSE; AC_PATH_PROGS() already does that.
 - Fix cleaning after previous builds by moving up builddir setting
   and only cleaning under $builddir/src/ so as not to launch infinite
   reruns of configure.

configure.in

@@ -16,8 +16,6 @@ AC_CHECK_PROG(ACLOCAL,[aclocal],[aclocal],[config/missing aclocal])
 AC_CHECK_PROG(AUTOCONF,[autoconf],[autoconf],[config/missing autoconf])
 AC_CHECK_PROG(AUTOHEADER,[autoheader],[autoheader],[config/missing autoheader])
 
-AC_PROG_MAKE_SET
-
 MAKE=
 
 for make in gnumake gmake make false; do
@@ -26,13 +24,15 @@ for make in gnumake gmake make false; do
 	fi
 done
 
+builddir="`pwd`"
+
 # Cleanup if we are configuring with a previous build in the tree
 if test -e Makefile.config; then
-	"$MAKE" -C "$builddir" cleanall  >/dev/null 2>/dev/null
+	AC_MSG_CHECKING([for previous build to clean])
+	"$MAKE" -C "$builddir/src" cleanall >/dev/null 2>/dev/null
+	AC_MSG_RESULT(done)
 fi
 
-builddir="`pwd`"
-
 dnl ===================================================================
 dnl Load feature configuration file and start logging features.
 dnl ===================================================================
@@ -53,9 +53,7 @@ AC_PROG_RANLIB
 AC_PROG_INSTALL
 
 AC_PATH_PROGS(CG_COMMIT_ID, "cg-commit-id")
-
 AC_PATH_PROGS(SPARSE, "sparse")
-AC_SUBST(SPARSE)
 
 CONFIG_ASCIIDOC="no"
 CONFIG_POD2HTML="no"