Remove deprecated GTK symbols

http://bugzilla.gnome.org/show_bug.cgi?id=587991

(adapted from metacity commit 3f76affbd2,
original patch by Thomas Andersen)

src/tools/mutter-window-demo.c

@@ -853,8 +853,7 @@ do_appwindow (void)
   item_factory = gtk_item_factory_new (GTK_TYPE_MENU_BAR, "<main>", accel_group);
 
   /* Set up item factory to go away with the window */
-  g_object_ref (item_factory);
-  gtk_object_sink (GTK_OBJECT (item_factory));
+  g_object_ref_sink (item_factory);
   g_object_set_data_full (G_OBJECT (window),
                           "<main>",
                           item_factory,