[WIP] Travis CI bundle cache

Trying to see how much a bundle cache will speed up the travis tests.

This PR uses the s3-put script as found here: http://mislav.uniqpath.com/2013/12/travis-cached-bundle/
I guess we could put it in the source but that's never how it's done.  Usually the bundle is saved offsite, and just pulled in for automated testing instead of installing gem by gem.  This bundle will be like 100+ MB, so having that in the repo doesn't seem good.