win32: Disable event retrieval in Cogl

Since commit 4543ed6ac3 in Cogl, Cogl will now try to consume
Windows message itself. This doesn't really cause any problems because
both message loops just call DispatchMessage which will cause the
message to be routed through Clutter's window procedure either way.
However, it's not great to have two sources listening for messages so
this patch disables Cogl's message retrieval.

https://bugzilla.gnome.org/show_bug.cgi?id=701356

clutter/gdk/clutter-backend-gdk.c

@@ -279,6 +279,7 @@ clutter_backend_gdk_get_renderer (ClutterBackend  *backend,
     {
       /* Force a WGL winsys on windows */
       cogl_renderer_set_winsys_id (renderer, COGL_WINSYS_ID_WGL);
+      cogl_win32_renderer_set_event_retrieval_enabled (renderer, FALSE);
     }
   else
 #endif