Python 3.4 is live on Travis CI

http://blog.travis-ci.com/2014-04-28-upcoming-build-environment-updates/
https://twitter.com/travisci/status/461365365587456000
system_site_packages was causing build errors. Allow 3.4 as a failure for now, as a PendingDeprecationWarning is causing failures; this is a problem with the test runner not liking any print output.
Add 3.4 back
Merge pull request #641 from hugovk/patch-1

Python 3.4 is live on Travis CI