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@.

xevents.c

@@ -290,7 +290,7 @@ xev_handle_buttonpress(struct xevent *xev, XEvent *ee)
 		if (TAILQ_EMPTY(&menuq))
 			goto out;
 
-		mi = (struct menu *)grab_menu(e, &menuq);
+		mi = menu_filter(&menuq, NULL, NULL, 0, NULL, NULL);
 		if (mi == NULL)
 			goto cleanup;