MenuShell: bind_model(): Make a parameter optional.
MenuShell: bind_model(): Make a parameter optional.

gmmproc will now generate a method overload without the
action_namespace parameter.

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