Use Glib::RefPtr<Glib::Source> in glib_integration_test. After the fix of bug https://bugzilla.gnome.org/show_bug.cgi?id=561885 Glib::Source::~Source is called when both  Source::unreference() and SourceCallbackData::destroy_notify_callback() are called.

	included in everything.

  which will invoke the destructor for the Glib::Source.
  
  Added an integration test to prove it
  
  (LP: #1085590)

restarts and shuts down