Move compositor-stack handling to MetaStackTracker

In order to properly track the stacking order for override-redirect
windows, move meta_compositor_sync_stack() call into MetaStackTracker.
In the new location, we sync the stack as a before-redraw idle function,
rather then using the freeze-thaw facilities of MetaStack. This is
simpler, and also properly compresses multiple stack changes on
notifications received from the X server.

http://bugzilla.gnome.org/show_bug.cgi?id=585984

src/core/window.c

@@ -1001,6 +1001,13 @@ meta_window_new_with_attrs (MetaDisplay       *display,
   /* Sync stack changes */
   meta_stack_thaw (window->screen->stack);
 
+  /* Usually the we'll have queued a stack sync anyways, because we've
+   * added a new frame window or restacked. But if an undecorated
+   * window is mapped, already stacked in the right place, then we
+   * might need to do this explicitly.
+   */
+  meta_stack_tracker_queue_sync_stack (window->screen->stack_tracker);
+
   /* disable show desktop mode unless we're a desktop component */
   maybe_leave_show_desktop_mode (window);
 
@@ -1309,6 +1316,12 @@ meta_window_unmanage (MetaWindow  *window,
   if (window->frame)
     meta_window_destroy_frame (window);
 
+  /* If an undecorated window is being withdrawn, that will change the
+   * stack as presented to the compositing manager, without actually
+   * changing the stacking order of X windows.
+   */
+  meta_stack_tracker_queue_sync_stack (window->screen->stack_tracker);
+
   if (window->withdrawn)
     {
       /* We need to clean off the window's state so it