Bug 851421 (part 1) - Clone extended function slots.  r=nnethercote.

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extra : rebase_source : c387da0c0ae5293fc36b76e84f5000fa17c100ce
Bug 851421 (part 2) - Don't emit bytecode for asm.js functions unless linking fails.  r=luke.

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extra : rebase_source : cbab73e8bad5d6153cfb1cdd7599c608e78fad8a