[cluttermm_tutorial] Replace deprecated Gtk::Main with Gtk::App

[Murray Cumming <murrayc src gnome org>]

commit 1dcc69d9fc1e7b3ad840bd8ead3fc1b819c230eb
Author: Murray Cumming <murrayc murrayc com>
Date:   Thu Apr 17 22:03:51 2014 +0200

    Replace deprecated Gtk::Main with Gtk::App

 examples/stage_widget/main.cc |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/examples/stage_widget/main.cc b/examples/stage_widget/main.cc
index a573e82..d5166fc 100644
--- a/examples/stage_widget/main.cc
+++ b/examples/stage_widget/main.cc
@@ -93,10 +93,10 @@ int main(int argc, char** argv)
   try
   {
     Clutter::Gtk::init(&argc, &argv);
-    Gtk::Main kit (&argc, &argv);
+    Glib::RefPtr<Gtk::Application> app = Gtk::Application::create(argc, argv, "org.gtkmm.example");
 
     StageWindow window;
-    Gtk::Main::run(window);
+    app->run(window);
   }
   catch (const Glib::Error& error)
   {