Add `racc` as dependency

Rubinius requires the explicit dependency on 'racc'.
(https://github.com/rubinius/rubinius/issues/2632#issuecomment-26954565)
Add rbx 2.1.1 to travis test suite

`rbx-19mode` is no longer used.
http://about.travis-ci.org/docs/user/languages/ruby/#Rubinius
Merge pull request #115 from coffeejunk/rbx

Test on rubinius