Add focusonactive patch to DWM

When an application tags itself as "active" i.e. has something to do,
this patch will ensure that we're focused on it.  Works on multiple
monitors!

dwm.c

@@ -571,6 +571,7 @@ clientmessage(XEvent *e)
 {
 	XClientMessageEvent *cme = &e->xclient;
 	Client *c = wintoclient(cme->window);
+	unsigned int i;
 
 	if (!c)
 		return;
@@ -585,8 +586,14 @@ clientmessage(XEvent *e)
 			setsticky(c, (cme->data.l[0] == 1 ||
 										(cme->data.l[0] == 2 && !c->issticky)));
 	} else if (cme->message_type == netatom[NetActiveWindow]) {
-		if (c != selmon->sel && !c->isurgent)
-			seturgent(c, 1);
+		for (i = 0; i < LENGTH(tags) && !((1 << i) & c->tags); i++);
+		if (i < LENGTH(tags)) {
+			const Arg a = {.ui = 1 << i};
+			selmon = c->mon;
+			view(&a);
+			focus(c);
+			restack(selmon);
+		}
 	}
 }