wmaker: Cleaned dangerous function prototype usage

- remove extern declaration in source file, use header instead

- add inclusion of header defining the functions of the file to
get the compiler to cross-check them

- marked static the functions that should not be visible ouside
their file

src/main.c

@@ -52,6 +52,7 @@
 #include "session.h"
 #include "shutdown.h"
 #include "dialog.h"
+#include "main.h"
 
 #include <WINGs/WUtil.h>