The switch to hGetMetered subtly changed the laziness of how DATA was
read, and broke git protocol relaying. Fix by sending received data to
the git process's stdin immediately, which ensures that the lazy
bytestring is all read from the peer before going on to process the next
message from the peer.
Display progress meter on send and receive from remote.
Added a new hGetMetered that can read an exact number of bytes (or
less), updating a meter as it goes.
This commit was sponsored by Andreas on Patreon.
It's possible, in direct or thin mode, that an object file gets
truncated or appended to as it's being sent. This would break the
protocol badly, so make sure never to send too many bytes, and to
close the protocol connection if too few bytes are available.
