Enable travis tests
Travis builds don't have SwapCached in meminfo
Add qtile Travis-ci status to README
Make Python 2.6 compatible

Dict comprehension and set literals are introduced in 2.7
Fix AttributeError recursion error
Fix test/test_command.py

Fix tests for commands added to CommandObject in
743a8a7be839bb1179580dd38f3e791ba7b839ab