finish unfucking the screen_ctx handling.

remove screen_current() it was utterly bogus when nscreens > 1.

pass a fake client_ctx in the case where there's no client and the
kbfunc or mousefunc doesn't need a real one, it just contains the
current screen, modify these functions so that they pass down the screen
context to their callees.

make groups per screen, it's the only way it makes sense in this regard.

ok okan@.

client.c

@@ -548,14 +548,12 @@ match:
 }
 
 struct client_ctx *
-client_cycle(int reverse)
+client_cycle(struct screen_ctx *sc, int reverse)
 {
 	struct client_ctx	*oldcc, *newcc;
-	struct screen_ctx	*sc;
 	int			 again = 1;
 
 	oldcc = client_current();
-	sc = screen_current();
 
 	/* If no windows then you cant cycle */
 	if (TAILQ_EMPTY(&sc->mruq))