Make wmaker XRandR aware

This patch makes wmaker automatically Restart() to take into account
resolution changes done by xrandr.

The motivation to write this patch is that when I start my laptop connected
to an external monitor (VGA1), the resolution in the monitor is initially
wrong (perhaps this is a bug in XOrg or OpenSuse, but anyway), so I always
do this after starting wmaker:

xrandr --output VGA1 --preferred

The resolution in the external monitor gets fixed, but wmaker does not
recognize the change automatically and I have to manually restart it.

So this patch avoids the last step by making wmaker be XRandR-aware.
Wmaker now restarts automatically when it receives a RRChangeScreenNotify
event and I don't have to do the last part of the silly procedure described
above.

I am not sure if restarting wmaker is the most elegant solution, but
it at least solves part of my issue with wmaker + xrandr.

src/screen.c

@@ -35,9 +35,11 @@
 #ifdef KEEP_XKB_LOCK_STATUS
 #include <X11/XKBlib.h>
 #endif				/* KEEP_XKB_LOCK_STATUS */
+#ifdef HAVE_XRANDR
+#include <X11/extensions/Xrandr.h>
+#endif
 
 #include <wraster.h>
-
 #include "WindowMaker.h"
 #include "def_pixmaps.h"
 #include "screen.h"
@@ -77,6 +79,9 @@ extern int wScreenCount;
 #ifdef KEEP_XKB_LOCK_STATUS
 extern int wXkbSupported;
 #endif
+#ifdef HAVE_XRANDR
+extern int has_randr;
+#endif
 
 extern WDDomain *WDWindowMaker;
 
@@ -598,6 +603,11 @@ WScreen *wScreenInit(int screen_number)
 	}
 #endif				/* KEEP_XKB_LOCK_STATUS */
 
+#ifdef HAVE_XRANDR
+	if (has_randr)
+		XRRSelectInput(dpy, scr->root_win, RRScreenChangeNotifyMask);
+#endif
+
 	XSync(dpy, False);
 	XSetErrorHandler(oldHandler);