Remove icon and menu from titlebar

To avoid visual duplication with the application menu, eliminate
the window menu button. (The window menu can still be accessed by
right-clicking on the title bar, or Alt-right-clicking anywhere on the
window.)

This is implemented using the new Mutter facility for GConf key
redirection; we add separate key for 'button_layout' with a default
that omits the menu button.

https://bugzilla.gnome.org/show_bug.cgi?id=591390

src/gnome-shell-plugin.c

@@ -139,6 +139,9 @@ static void
 gnome_shell_plugin_init (GnomeShellPlugin *shell_plugin)
 {
   _shell_global_set_plugin (shell_global_get(), MUTTER_PLUGIN(shell_plugin));
+
+  meta_prefs_override_preference_location ("/apps/metacity/general/button_layout",
+                                           "/desktop/gnome/shell/windows/button_layout");
 }
 
 static void