Bug 1095973 - Fix crash @PurgeProtoChain introduced by 1090537. r=efaust.

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extra : rebase_source : a2e90c7ffd69dddee190a4de927fe68cb52482dd
Bug 1095973, epilogue - Tweaks to PurgeProtoChain/PurgeScopeChain and a jit-test for the invariant enforced by PurgeProtoChain. r=efaust.

--HG--
extra : rebase_source : 6f0e1a4d7573fdcdc45962a63d30bf6ee480d3be
Bug 1058252 - Use of uninitialized value in DOMProxyHandler::delete_. r=bz.

--HG--
extra : rebase_source : cc8437789c3a9e307c4ba851ded49a7d2afd538d
Bug 1066322 - Enable ES6 symbols in all builds. r=jandem.

--HG--
extra : rebase_source : 49654e9105657b17862e3fed97ec4878d9373447
Bug 1094062 - Delete js/public/PropertyKey.h. r=jandem.

--HG--
extra : rebase_source : 4ff841a634f08f611529d18878074d6dc73d0fd3