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/workspace.c

@@ -61,7 +61,6 @@
 extern int ignore_wks_change;
 extern WPreferences wPreferences;
 extern XContext wVEdgeContext;
-extern void ProcessPendingEvents();
 extern WShortKey wKeyBindings[WKBD_LAST];
 
 static WMPropList *dWorkspaces = NULL;