Change set literals with {...} to set([...]) for Py2.6 compatibility
Remove two unnecessary imports
Monkey-patch a subprocess.check_output fn on Py2.6
Allow test discovery on Py26 with unittest2
Use unittest2 on Python 2.6
Convert '{}'.format() to '{0}'.format() for Python 2.6 compatibility
Python 2.6 fixes for test.support
Improve Py2.6 compatibility for newbytes.__new__ with encoding arg
Fix Py3 SyntaxError with one xfailing test (test_problematic_string)
Remove @skipIf decorators that attempt to prevent spurious travis-ci failures; add a manual test skipping mechanism

- The decorators weren't solving the problem: see e.g. https://travis-ci.org/PythonCharmers/python-future/jobs/13129148