Bug 909178 (part 1) - Move |jsid| from jsapi.h into js/Id.h.  r=luke.

--HG--
extra : rebase_source : b0d38093a9f40a532e73c2c30ae86b8970b814ac
Bug 909178 (part 2) - Make jsclass.h not depend on jsapi.h, and rename it js/Class.h.  r=jwalden.

--HG--
rename : js/src/jsclass.h => js/public/Class.h
extra : rebase_source : 31ecd4074181c234f7f71eef04a10ae371c35eaa