add "test:rails4units", "test:rails4functionals" and "test:rails4integration" rake tasks

--HG--
branch : rails4.20140214
.travis.yml: use rails4* tests

--HG--
branch : rails4.20140214
Gemfile: use awesome_nested_set pull requests

* https://github.com/collectiveidea/awesome_nested_set/pull/234
* https://github.com/collectiveidea/awesome_nested_set/pull/235
* https://github.com/collectiveidea/awesome_nested_set/pull/242