Adding unsafeShiftL, unsafeShiftR to Data.Bits(Bits)

Johan Tibell has proposed that we add unsafeShiftL and unsafeShiftR methods to the Bits class, as per the patch here: http://hackage.haskell.org/trac/ghc/attachment/ticket/5414/0001-Add-unsafeSh... I've talked this through with Johan, and we came to the conclusion that while "unsafeShiftL" is a bit unsightly, this is the most workable solution. For example, optimising away the test in shiftL directly in the backend is not possible when compiling via LLVM, which only provides the unsafe operation as a primitive. Any objections before I push this in? Cheers, Simon