Summary:
This need a bunch of work, but is a sort of minimum viable product for the hgdaemon.
The two ProtocolChannels implement the client and server halves of the protocol.
The Server implements the server logic, the Client implements the client logic.
Test Plan: Launched a server and client on the same repo, got hg output in ~2-3ms instead of 100ms+.
Reviewers: csilvers, btrahan, vrana
Reviewed By: csilvers
CC: aran
Differential Revision: https://secure.phabricator.com/D2665
