Bug 891209 (part 1) - Change TOK_ERROR from -1 to 0 so that TokenKind values can be used to index into arrays.  r=jorendorff.

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extra : rebase_source : 197cfb12f68da77496aa1dae67261b8b48def897
Bug 891209 (part 2) - Parse "detectably simple" expressions quickly.  r=jorendorff.

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extra : rebase_source : c501dc470978a94898fd68311b776574034fb654