Test against rails v3.2 and v4.0 with appraisal

- Add appraisal gem
- Ignore generated gemfile.lock
- Test against rails4.0
- Test with generated gemfile for travis-ci
    - Use still original Gemfile and Gemfile.lock

https://rubygems.org/gems/appraisal
https://github.com/thoughtbot/appraisal