Port the TCP transport to the new stream API
Port HTTP(S) to the new stream API
ssh: use socket_stream to perform the connection

Having an ssh stream would require extra work for stream capabilities we
don't need anywhere else (oob auth and command execution) so for now
let's move away from the gitno connection to use socket_stream.

We can introduce an ssh stream interface if and as we need it.
gitno: remove code which is no longer needed

Most of the network-facing facilities have been copied to the socket and
openssl streams. No code now uses these functions directly anymore, so
we can now remove them.
stream: constify the write buffer