Multiple Rails versions in specs, update Travis, add JRuby to specs

1. Updated the specs so they can run against Rails 3.1.x, 3.2.x, and 4.0.x
2. Update Travis CI config to start Redis service
3. Update Travis CI to run specs against all supported Rails minor versions
4. Changes to gemspec to allow use of JRuby in specs
5. Add JRuby to Travis
6. Add lockfiles to .gitignore