remove pwin, bringing us to one client, one window. we no longer have

to push attributes around, so things get a lot simplier, while fixing a
few issues in the meantime; original suggestion by Edd Barrett many many
moons ago.

annoying window placement and race, found in c2k8 by todd, fix by oga!

lots of feedback from todd and oga - thanks!

"commit that bad boy" oga@

group.c

@@ -99,7 +99,7 @@ _group_show(struct group_ctx *gc)
 	 * top-to-bottom.
 	 */
 	TAILQ_FOREACH(cc, &gc->clients, group_entry) {
-		winlist[gc->highstack - cc->stackingorder] = cc->pwin;
+		winlist[gc->highstack - cc->stackingorder] = cc->win;
 		client_unhide(cc);
 	}