dtwm: Cleanup some implicit definitions

Mostly this is adding appropriate #includes and declarations,
but for WmImage.c we also change from using the proper name
for XmeGetMask, rather than the identical but renamed
version _DtGetMask which is not exported in any header.

cde/programs/dtwm/WmParse.c

@@ -66,6 +66,7 @@ static char rcsid[] = "$XConsortium: WmParse.c /main/5 1996/10/30 11:36:06 drk $
 #ifdef MULTIBYTE
 #include <stdlib.h>
 #endif /* MULTIBYTE */
+#include <ctype.h>
 
 /*
  * Internal routines