Fix deleted file representation with new gitlab_git gem

Added this MR as per request from https://github.com/gitlabhq/gitlabhq/pull/7980

* Add new gitlab_gem as per gitlab-org/gitlab_git!6
* Fix the showing of deleted file, as it only displays the named of the file, rather than specifying what had happened

**Before**

![Screen Shot 2014-12-30 at 21.02.55](https://gitlab.com/uploads/arif-ali/gitlab-ce/67ec88b06d/Screen_Shot_2014-12-30_at_21.02.55.png)

**After**

![Screen Shot 2014-12-30 at 21.05.18](https://gitlab.com/uploads/arif-ali/gitlab-ce/050b689c82/Screen_Shot_2014-12-30_at_21.05.18.png)

See merge request !273