Redirect auto-gc output to the sideband such that it is visible to all
clients. As a side effect, all auto-gc error messages are now prefixed
with "remote: " before being printed to stderr on the client-side which
makes it easier to understand that those error messages originate from
the server.
Signed-off-by: Lukas Fleischer <lfleischer@lfos.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>