Add possibility to download .patch/.diff from merge request versions
GitLab stores merge request internally, but there's no way to retrieve these.
Example, i've tried:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/22330/diffs?diff_id=25004746.patch
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/22330/diffs?diff_id=25004746.diff
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/22330.diff?diff_id=25004746
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/22330.patch?diff_id=25004746
See context: