Natural-born citizenship is no guarantee of being treated humanely. Case in point: Black folk harassed and rejected like immigrants in Lynn Nottage’s stunningly absorbing play, “Crumbs from the Table of Joy.” A grieving father and his two daughters emigrate from Florida to Brooklyn, whose complexities are foreign not only to them but also to most of us. Surrounded by an entirely white world, four Black characters struggle for acceptance, inner strength and equality. No wonder…