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/main.c

@@ -143,6 +143,11 @@ Bool wXkbSupported;
 int wXkbEventBase;
 #endif
 
+#ifdef HAVE_XRANDR
+Bool has_randr;
+int randr_event_base;
+#endif
+
 /* special flags */
 char WProgramSigState = 0;
 char WProgramState = WSTATE_NORMAL;