Support for gitlab-git-http-server got merged upstream:
https://gitlab.com/gitlab-org/gitlab-ce/commit/d64ae5363fc17bf5592bc1a66a53763ddb9a3acc

Supposedly they are not idiomatic!

The path must exist and not contain '/../' (traversal).

I am no 100% sure but I think we can only write the HTTP status
code once. So once the 200 is out, we might as well panic on errors.
The Go HTTP server will only let the goroutine crash, not the entire
server process.