make numpy a requirement only if not already installed
make numpy a requirement only if not already installed

rootpy/root_numpy,scikit-hep/root_numpy,ndawe/root_numpy,scikit-hep/root_numpy,ndawe/root_numpy,rootpy/root_numpy,rootpy/root_numpy,ndawe/root_numpy,scikit-hep/root_numpy,rootpy/root_numpy,ndawe/root_numpy,scikit-hep/root_numpy