Bug 935789, part 1: Kill most uses of prbit.h, r=ehsan

--HG--
extra : rebase_source : 4c44e60c72e0ece3cea7ed1cf79079bd2a1b6487
Bug 935789, part 2: Implement RotateLeft/RotateRight in MFBT and use them, r=Waldo.

--HG--
extra : rebase_source : efda8cfde4ec1b8cee007f528d682830f43f9111