Assistant: Wrap new ::use-header-bar property
Assistant: Wrap new ::use-header-bar property

	* Add ::use-header-bar read-only property

johne53/MB3Gtkmm,GNOME/gtkmm,GNOME/gtkmm,johne53/MB3Gtkmm,johne53/MB3Gtkmm,GNOME/gtkmm,GNOME/gtkmm