Bug 898914 (part 1) - Remove JSBool.

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extra : rebase_source : 2d202e0e5005a7f54724b1540481c15cde3ad52e
Bug 898914 (part 2) - Avoid some bool shuffling.

--HG--
extra : rebase_source : 7db1df2a4ebb24a97860abb48c490348a6ca8de1