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/WmWrkspace.h

@@ -39,6 +39,7 @@ static char rcsid[] = ""
 
 extern void ChangeToWorkspace( 
                         WmWorkspaceData *pNewWS) ;
+extern void ChangeWorkspaceTitle( WmWorkspaceData *pWS, char * pchTitle);
 extern Boolean DuplicateWorkspaceName (
 			WmScreenData *pSD, 
 			unsigned char *name,