dix: add screen hook for post-window-destroy

In contrast to the already existing WindowDestroy hook, this one is
called *after* the driver's DestroyWindow() proc.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>

include/scrnintstr.h

@@ -700,6 +700,10 @@ typedef struct _Screen {
     /* additional screen post-close notify hooks (replaces wrapping CloseScreen)
        should NOT be touched outside of DIX core */
     CallbackListPtr hookPostClose;
+
+    /* additional post window destructors (replaces wrapping DestroyWindow).
+       should NOT be touched outside of DIX core */
+    CallbackListPtr hookPostWindowDestroy;
 } ScreenRec;
 
 static inline RegionPtr