Merge pull request #188 from hesselink/master

Add users to uploaders group after signup.
Use travis_retry to reduce false negative test results on Travis

See http://blog.travis-ci.com/2013-05-20-network-timeouts-build-retries/

Thanks to Mateusz Kowalczyk for the tip.
Merge pull request #192 from ian-ross/travis-retry

Use travis_retry to reduce false negative test results on Travis
Only retry cabal test for the moment in travis config

Travis seems to have random network problems and their current recommended workaround is to retry a few times. I think we only want to do this for the tests (which is where we've seen the problems) and not for the main code compile check (where we'd end up getting the same build failure three times or whatever).