Bug 973238 Part 4 -- Use prototype rather than reserved slot to uncover descriptor r=jandem
Bug 973238 Part 5 -- Remove private field from StructTypeDescr, which is unused r=sfink
Bug 973238 Part 6 -- Consult prototype rather than typed object addendum r=bhackett
Bug 973238 Part 7 -- Remove type object addendum; leave the addendum mechanism in place r=bhackett