Fix SDL fullscreen problems when the resolution changes:
https://groups.google.com/d/msg/wmii/nJBrSjrnnq8/ZEYWOWE5pj4J

diff -r ec4baab78314 dwm.c
--- a/dwm.c	Mon Dec 19 15:38:30 2011 +0100
+++ b/dwm.c	Sat Jan 14 12:35:50 2012 +0100
@@ -397,9 +397,10 @@
 		showhide(m->stack);
 	else for(m = mons; m; m = m->next)
 		showhide(m->stack);
-	if(m)
+	if(m) {
 		arrangemon(m);
-	else for(m = mons; m; m = m->next)
+		restack(m);
+	} else for(m = mons; m; m = m->next)
 		arrangemon(m);
 }
 
@@ -408,7 +409,6 @@
 	strncpy(m->ltsymbol, m->lt[m->sellt]->symbol, sizeof m->ltsymbol);
 	if(m->lt[m->sellt]->arrange)
 		m->lt[m->sellt]->arrange(m);
-	restack(m);
 }
 
 void
@@ -1827,6 +1827,8 @@
 		.event_mask = ButtonPressMask|ExposureMask
 	};
 	for(m = mons; m; m = m->next) {
+		if (m->barwin)
+			continue;
 		m->barwin = XCreateWindow(dpy, root, m->wx, m->by, m->ww, bh, 0, DefaultDepth(dpy, screen),
 		                          CopyFromParent, DefaultVisual(dpy, screen),
 		                          CWOverrideRedirect|CWBackPixmap|CWEventMask, &wa);