Fixes for dispose and finalize

* Add missing chain-up for dispose and finalize methods
* ShellGenericContainer needs to destroy its children in dispose()
* Fix variable naming and excess casts in st_label_dispose()

https://bugzilla.gnome.org/show_bug.cgi?id=612511

src/shell-app.c

@@ -360,6 +360,8 @@ shell_app_dispose (GObject *object)
     _shell_app_remove_window (app, app->windows->data);
 
   disconnect_workspace_switch (app);
+
+  G_OBJECT_CLASS(shell_app_parent_class)->dispose (object);
 }
 
 static void