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/monitor.c

@@ -43,7 +43,7 @@
 /****** Global Variables ******/
 extern WPreferences wPreferences;
 
-int showCrashDialog(int sig)
+static int showCrashDialog(int sig)
 {
 	int crashAction;