Add Mislav Marohnić's cached-bundle scripts

Per http://mislav.uniqpath.com/2013/12/travis-cached-bundle/
Get cached-bundle script to run

* Fix environment variables
* Fix script permissions
* Ignore script directory and files when checking against extra files
Clean up cached-bundle caching

* change bundle location
* remove cache archive after installation
* install nokogiri with system libraries again, if needed
* remove some redundant parameters on cached-bundle call