Another Python 3 fix--definitely should be inserting ASCII-encoded bytes here, not unicode strings.  Not sure exactly why this didn't blow up sooner.
Another Python 3 fix--definitely should be inserting ASCII-encoded bytes here, not unicode strings.  Not sure exactly why this didn't blow up sooner.

git-svn-id: 5305e2c1a78737cf7dd5f8f44e9bbbd00348fde7@2486 ed100bfc-0583-0410-97f2-c26b58777a21

embray/PyFITS,embray/PyFITS,embray/PyFITS,spacetelescope/PyFITS,embray/PyFITS,spacetelescope/PyFITS