updated the 3.0.0-wip branch

- Updated the 3.0.0-wip branch with latest changes from https://github.com/twbs/bootstrap/tree/3.0.0-wip
- Updated the scripts/update_bootstrap.sh with the one from https://github.com/metaskills/less-rails-bootstrap/tree/3.0.0-rc1
- Updated the twitter/bootstrap repository in README.md