Integrate testing with browserstack runner

We are BrowserStack and have made a npm package https://github.com/browserstack/browserstack-runner to enable easy Cross Browser Testing of open source JS libraries. The idea is:
1. These JS libraries can be cross browser tested
2. Make it super easy to test cross browser compatibility. (for eg. all you need is to provide a config file with supported browsers, test files) 

This pull request enables browser testing for bootstrap (3.0.0-wip as of now). The current build can be seen here: https://travis-ci.org/browserstack/bootstrap

I will send more details over to @mdo