util: Created header to define functions that may be used in more that one place

Using local function prototype redefinition is dangerous, now the
prototype is seen in all concerned files.

util/getstyle.c

@@ -40,6 +40,8 @@
 
 #include <WINGs/WUtil.h>
 
+#include "common.h"
+
 #define	RETRY( x )	do {				\
 				x;			\
 			} while (errno == EINTR);
@@ -135,7 +137,6 @@ WMPropList *PixmapPath = NULL;
 
 char *ThemePath = NULL;
 
-extern char *convertFont(char *font, Bool keepXLFD);
 
 void print_help(int print_usage, int exitval)
 {