let travis-ci test the code :)
install swig/augeas et al.
split test matrix to cover py26 and lint separately
travis-ci: install extras[testing]
add travis-ci badge to readme
Merge remote-tracking branch 'github/letsencrypt/master' into pr/85

Conflicts:
	README.md
Travis CI: remove python version, use setup.py dev[testing]
Use travis_retry.

http://blog.travis-ci.com/2013-05-20-network-timeouts-build-retries
Travis: fix YAML style
Travis: explicit -e $TOX_ENV not necessary
Travis: multiple Python environments.
Fix dev[testing] typo in .travis.yml
TOXENV instead of TOX_ENV

http://tox.readthedocs.org/en/latest/config.html?highlight=toxenv#confval-envlist=CSV
Remove unnecessary "Build status" comment
Merge pull request #96 from kuba/pr/85

#85 fixup/cleanup (travis)