Mostly ripped from D7391, with some changes:
- Serve repositories at /diffusion/X/, with no special /git/ or /serve/ URI component.
- This requires a little bit of magic, but I got the magic working for Git, Mercurial and SVN, and it seems reasonable.
- I think having one URI for everything will make it easier for users to understand.
- One downside is that git will clone into X by default, but I think that's not a big deal, and we can work around that in the future easily enough.
- Accept HTTP requests for Git, SVN and Mercurial repositories.
- Auth logic is a little different in order to be more consistent with how other things work.
- Instead of AphrontBasicAuthResponse, added "VCSResponse". Mercurial can print strings we send it on the CLI if we're careful, so support that. I did a fair amount of digging and didn't have any luck with git or svn.
- Commands we don't know about are assumed to require "Push" capability by default.
No actual VCS data going over the wire yet.