Bug 918828, part 1 - Change iteration code to call iterable[Symbol.iterator]() rather than iterable["@@iterator"](). r=Waldo with earlier review work by nbp.

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extra : rebase_source : 5780eed342b1780570650d140c7f14f966b7f1e1
Bug 918828, part 2 - Update decompiler for JSOP_SYMBOL. This improves error messages when @@iterator is called implicitly. r=Waldo.

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extra : rebase_source : e0e00a4d203f3a2c8a4d7cfa0a53d389e16fec53
Bug 918828, part 3 - Implement JSOP_SYMBOL in the baseline compiler. r=nbp.

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extra : rebase_source : 387d627e74cf447014805b901e42ee201f513ea0
Bug 1089758 - EmitElemOpBase's automagical JSOP_SWAP is too magical. r=Waldo.

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extra : rebase_source : a4c052ff028b81556978398c401f3ace74d8c822
Bug 1090325 - Fix unconditional Symbol usage in a test, introduced by rev bff9837442af. r=Waldo.

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extra : rebase_source : 6301cee87494e1d64ed42a32247e62a2f984a3f0