clone: disconnect transport after fetching

The current code just leaves the transport in whatever state it was in after performing the fetch. For a non-empty clone over the git protocol, the transport code already disconnects at the end of the fetch. But for an empty clone, we leave the connection hanging, and eventually close the socket when clone exits. This causes the remote upload-pack to complain "the remote end hung up unexpectedly". While this message is harmless to the clone itself, it is unnecessarily scary for a user to see and may pollute git-daemon logs. This patch just explicitly calls disconnect after we are done with the remote end, which sends a flush packet to upload-pack and cleanly disconnects, avoiding the error message. Other transports are unaffected or slightly improved: - for a non-empty repo over the git protocol, the second disconnect is a no-op (since we are no longer connected) - for "walker" transports (like HTTP or FTP), we actually free some used memory (which previously just sat until the clone process exits) - for "rsync", disconnect is always a no-op anyway Signed-off-by: Jeff King <peff@peff.net> Acked-by: Daniel Barkalow <barkalow@iabervon.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>