Add git-salt module.

Add an initial communication between CDE and git-nacl port (`git-salt`).

1) This enables a `git-clone` powered by nacl behind a flag.
2) This is still a work in progress, and lot of things may be broken.
3) Some debug logs are left intentionally, will be cleaned in future.

Did all this logging plumbing come from sample code?  It doesn't seem terribly useful here.