Add first cut at "git protocol" connect logic.

Add first cut at "git protocol" connect logic.

Useful for pulling stuff off a dedicated server.  Instead of connecting
with ssh or just starting a local pipeline, we connect over TCP to the
other side and try to see if there's a git server listening.

Of course, since I haven't written the git server yet, that will never
happen.  But the server really just needs to listen on a port, and
execute a "git-upload-pack" when somebody connects.

(It should read one packet-line, which should be of the format

	"git-upload-pack directoryname\n"

and eventually we migth have other commands the server might accept).