Reorder shuffle and binary operation.

This patch enables transformations:

    BinOp(shuffle(v1), shuffle(v2)) -> shuffle(BinOp(v1, v2))
    BinOp(shuffle(v1), const1) -> shuffle(BinOp, const2)

They allow to eliminate extra shuffles in some cases.

Differential Revision: http://reviews.llvm.org/D3525