Recify 54ed32c1c3c1e16de34a212d5621fe824746af3b which was written before 92aab898f9ea64bac1dfc64531af7346e48213e8--the __repr__ and __str__ still relied on the SIP and InverseSIP models being based on the composite model class which is no longer the case.
Merge branch 'master' of github.com:astropy/astropy