Replace pyfits dependency with astropy.io.fits

[gregreen]

The module pyfits has been merged into astropy, and is no longer under active development outside of astropy. For all intents and purposes, pyfits now lives at astropy.io.fits, and many users will no longer have pyfits independently installed. One solution to this problem, which I use in my own scripts, is to replace all import pyfits statements with the following:

try:
    import astropy.io.fits as pyfits
except ImportError:
    import pyfits

Could you make this change?

[gregreen]

Sorry, I see you addressed issue in the branch anaconda-updates. Maybe it's time for a merge into master.