fix dist compilation failure

remove illegal wcwidth.c include and compile wcwidth.c
correct #include in wcwidth.c
fallout from #480

src/core/Makefile.am

@@ -45,6 +45,7 @@ libcore_a_SOURCES = \
 	signals.c \
 	special-vars.c \
 	utf8.c \
+	wcwidth.c \
 	write-buffer.c
 
 structure_headers = \
@@ -94,6 +95,7 @@ pkginc_core_HEADERS = \
 	settings.h \
 	signals.h \
 	special-vars.h \
+	utf8.h \
 	window-item-def.h \
 	write-buffer.h \
 	$(structure_headers)

src/core/utf8.c

@@ -24,7 +24,7 @@
 
 #include "utf8.h"
 #include "module.h"
-#include "wcwidth.c"
+
 /* Provide is_utf8(): */
 #include "recode.h"
 

src/core/wcwidth.c

@@ -59,7 +59,7 @@
  * Latest version: http://www.cl.cam.ac.uk/~mgk25/ucs/wcwidth.c
  */
 
-#include "module.h"
+#include "utf8.h"
 
 struct interval {
   int first;