Implemented nextafter and llvm.memset.
Implemented nextafter and llvm.memset.

bitfusionio/Oclgrind,surround-io/oclgrind,surround-io/oclgrind,surround-io/oclgrind,surround-io/oclgrind,mpflanzer/Oclgrind,mpflanzer/Oclgrind,bitfusionio/Oclgrind,bitfusionio/Oclgrind,mpflanzer/Oclgrind,bitfusionio/Oclgrind,mpflanzer/Oclgrind