ERRASER script converting python versions results in spurious diffs

[everyday847]

So, there's this pair of scripts in ERRASER: convert_to_phenix_python and convert_to_sys_python. There are two issues:

1. The sed syntax is platform dependent. I don't think sed -i 's/env python/env phenix.python/g' *.py works on Macs. (At least, it gives me sed: 1: "SWA_rebuild.py": invalid command code S and I do think there's a platform dependence, from what I remember.)
2. You cannot use these scripts in a checkout of the repo where you are doing any development work or you will commit spurious changes. The files it changes are versioned, after all.

[everyday847]

sed -i -e seems to be cross platform, btw