So we still commit outside the hooks, and only
update ref inside the hooks. There are only two
exceptions:

* Whenever it's adding a tag. We can't add a tag
  without committing, unfortunately. See !7700
* Whenever source project is in another repository.
  We'll need to fetch ref otherwise commits can't be made.

See the whole discussion starting from:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7237#note_19210942