Bug 996076: Preparatory clean-ups, factor out error code; r=nmatsakis
Bug 996076: Add SIMD.int32x4.{equal,greaterThan,lessThan} to the interpreter; r=nmatsakis
Bug 996076: Add SIMD.float32x4.{not,and,or,xor} to the interpreter; r=nmatsakis

--HG--
extra : histedit_source : d7bc3ddbf27314c5a2256c838b3e844cace2630f
Bug 996076: Add SIMD.int32x4.{shiftLeft,shiftRight,shiftRightLogical} to the interpreter; r=nmatsakis

--HG--
extra : amend_source : 10d086a2af141bc10d0646b87ccf1b81ecc5fb3e
extra : histedit_source : 16d5d4a0cd5db66621030ff078227fb36d1d5ff8