Live previews for hidden windows.

ClutterActors for hidden windows (such windows on different than active
workspaces and windows that are minimized) are available, and reflect the
actual state of the window. This is intended for use in task-switchers etc.

This feature is disabled by default (due to increased demand on resources),
and can be enabled through the metacity/general/live_hidden_windows gconf key.

A trivial sample window switcher is included in the scratch plugin (activated
by clicking on the slide out panel).

src/core/screen.c

@@ -772,6 +772,17 @@ meta_screen_manage_all_windows (MetaScreen *screen)
     }
   meta_stack_thaw (screen->stack);
 
+  /*
+   * Because the windows have already been created/mapped/etc, if the compositor
+   * maintains a separate stack based on ConfigureNotify restack messages, it
+   * will not necessarily get what it needs; we explicitely notify the
+   * compositor to fix up its stacking order.
+   *
+   * For more on this issue, see comments in meta_window_hide().
+   */
+  if (screen->display->compositor)
+    meta_compositor_ensure_stack_order (screen->display->compositor, screen);
+
   g_list_foreach (windows, (GFunc)g_free, NULL);
   g_list_free (windows);