Gtk::Application::make_window_and_run(): Delay the deletion
Gtk::Application::make_window_and_run(): Delay the deletion

Let Gtk::Object::destroy_notify_() delete the created C++ wrapper
(a Gtk::Window or a descendant of Gtk::Window) when the underlying
C instance is destroyed. Signal handlers such as on_unrealize()
are then called before the C++ wrapper is deleted. Fixes #114

GNOME/gtkmm,GNOME/gtkmm,GNOME/gtkmm,GNOME/gtkmm