MacOS 10.8 test failures with Python 3.1

The Mac Jenkins machine was offline for a week, and now it's back up it's showing a few test failures with Python 3.1:

https://jenkins.shiningpanda.com/astropy/job/astropy-master-osx-10.8-multiconfig/

These are related to the new ``compose`` functionality implemented by @mdboom last week. Travis no longer has 3.1 installed, so maybe that's why we didn't see it sooner.