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

Performance improvement
Merge branch 'master' of git://github.com/astropy/astropy into docs
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
Merge branch 'master' of git://github.com/astropy/astropy into docs