Delay HTTP headers for Git HTTP responses

Alternative to https://gitlab.com/gitlab-org/gitlab-workhorse/merge_requests/38
and https://gitlab.com/gitlab-org/gitlab-workhorse/merge_requests/40 .

See merge request !42

Add test guidelines



See merge request !39

Set content-length when sending git blobs

This gives the HTTP client receiving the blob a way to detect some
transmission failures.

See merge request !41

This gives the HTTP client receiving the blob a way to detect some
transmission failures.

Handle "git archive" via headers

Companion to https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/2675

See merge request !36

Unset Content-Length for raw Git blobs

Fixes https://gitlab.com/gitlab-org/gitlab-workhorse/merge_requests/30#note_3560130

Failure to get raw Git blob via /api/v3 with error:

error: SendBlob: copy git cat-file stdout: Conn.Write wrote more than the declared Content-Length

See merge request !37

Blobs via workhorse

Works together with https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/2451

See merge request !30

This is meant as an extra layer of defense against untrusted user
input.

Fixed typo



See merge request !35