Fix resize with multiple monitors and portrait mode

When connecting/disconnecting a portrait monitor, the
XRRScreenChangeNotifyEvent height & width are reversed due to the XRandR
rotation; detect this and DTRT.

slock.c

@@ -201,6 +201,11 @@ readpw(Display *dpy, struct xrandr *rr, struct lock **locks, int nscreens,
 			rre = (XRRScreenChangeNotifyEvent*)&ev;
 			for (screen = 0; screen < nscreens; screen++) {
 				if (locks[screen]->win == rre->window) {
+					if (rre->rotation == RR_Rotate_90 ||
+					    rre->rotation == RR_Rotate_270)
+						XResizeWindow(dpy, locks[screen]->win,
+						              rre->height, rre->width);
+					else
 						XResizeWindow(dpy, locks[screen]->win,
 						              rre->width, rre->height);
 					XClearWindow(dpy, locks[screen]->win);