Merge branch 'post-receive-base64' into 'master'

Prevent gitlab-shell character encoding issues by receiving its changes as raw data.

Depends on gitlab/gitlab-shell!65.

Fixes:

- https://github.com/gitlabhq/gitlabhq/issues/7486
- https://gitlab.com/gitlab-org/gitlab-ce/issues/858
- https://gitlab.com/gitlab-org/gitlab-ce/issues/877
- https://gitlab.com/gitlab-org/gitlab-ce/issues/965

See merge request !1701