Make menu_filter handle mouse movement too. This enables the keyboard

search dialogues to be manipulated with the mouse, too. It also allows
me to shrink the codebase further by killing grab_menu().

One known issue with highlighting the first entry in a search dialogue,
that'll be fixed soonish.

ok okan@, tested by Edd Barrett and todd@.

group.c

@@ -273,7 +273,7 @@ group_menu(XButtonEvent *e)
 	if (TAILQ_EMPTY(&menuq))
 		return;
 
-	mi = (struct menu *)grab_menu(e, &menuq);
+	mi = menu_filter(&menuq, NULL, NULL, 0, NULL, NULL);
 
 	if (mi == NULL || mi->ctx == NULL)
 		goto cleanup;