R1:f9a5cd2bbd86

Fix all remaining weird Diffusion request processing

Summary: Ref T4245. This is the last of it, and covers the clone/push stuff.

Test Plan:
- Cloned git.
- Pushed git.
- Cloned mercurial.
- Pushed mercurial.
- Visited a `blah.git` URL in my browser just because; got redirected to a human-facing UI.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T4245

Differential Revision: https://secure.phabricator.com/D14949