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.