Allow Phabricator to serve Mercurial repositories over HTTP
Summary: Ref T2230. This is easily the worst thing I've had to write in a while. I'll leave some notes inline.
Test Plan: Ran hg clone http://... on a hosted repo. Ran hg push on the same. Changed sync'd both ways.
Reviewers: asherkin, btrahan
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T2230
Differential Revision: https://secure.phabricator.com/D7520