If someone responded with a negative (n|no) to the confirmation,
then the Message-ID of the discarded email is no longer used
in the References: header of subsequent emails.
Consequently, send_message() now returns 1 if the message was
sent and 0 otherwise.
Signed-off-by: Michael Witten <mfwitten@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>