Updates OS X installation page with new variable PV_OPENMP_COMPILER_FLAG
Updates OS X installation page with new variable PV_OPENMP_COMPILER_FLAG

dpaiton/OpenPV,PetaVision/OpenPV,dpaiton/OpenPV,dpaiton/OpenPV,dpaiton/OpenPV,dpaiton/OpenPV,dpaiton/OpenPV,PetaVision/OpenPV,dpaiton/OpenPV,PetaVision/OpenPV,PetaVision/OpenPV,PetaVision/OpenPV,dpaiton/OpenPV