Merge branch 'pyfits/astropy' into astropy

Merges up through r2181 from pyfits' SVN (still need to update the
astropy changelog with the relevant changes as well).

Before merging this I still want to add a changelog entry, but otherwise it looks good (passing all the tests locally at least).

This should fix #755, #958, and #994, among other issues that were reported on the pyfits end.