Some tests fail only in py2.6:
https://travis-ci.org/wikimedia/pywikibot-core/jobs/27558463
(
https://gerrit.wikimedia.org/r/139591/ is an attempted fix).
But I think we may instead drop support for py2.6 entirely, focusing
ourselves on py2.7 ? py3k.
* no more need for external dependencies like
https://gerrit.wikimedia.org/r/138318
* less work for Travis-CI
* new features like dict comprehension, etc.