reverse order of operands
improve logic
correct inverse and start a new Travis build.
Merge pull request #1353 from nden/performance-improvement

Performance improvement
503e3ebc inadvertently introduced code that is not compatible with
Python 2.6 (subprocess.check_output).  This remedies that.
Fix subprocess.check_output on early Python 2.6
Make sure we have an old and working py.test installed, as a temporary measure
Only upgrade numpy -- everything else should use the specified versions.
Merge pull request #1501 from mdboom/downgrade-pytest

Attempt to fix Travis after pytest 2.4.0 upgrade
Make tests compatible with pytest 2.4.0
Merge pull request #1503 from mdboom/testing/pytest-2.4.0

Make tests compatible with pytest 2.4.0
Merge branch 'master' of git://github.com/astropy/astropy into docs