we don't have non-menu ToggleButtons yet, so thats not done here.

since we first started with GtkPushButton:menu_attrib to indicate
menubuttons gtk has grown menu buttons, but they don't have the
idea of a gtktogglemenu button, so this attribute still has a role
to play I guess

Change-Id: Iebfe5ccf996e22784cf9aaf2bcf367eed79ae686