EntryCompletion: Add the no_matches signal.
EntryCompletion: Add the no_matches signal.

With no default handler, to avoid breaking ABI.

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