We used to write "Message-Id:" and "Message-ID:" pretty much
interchangeably, and the header name is defined to be case
insensitive by the RFCs, but the canonical form "Message-ID:" is
used throughout the RFC documents, so let's imitate it ourselves.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Reviewed-by: Elijah Newren <newren@gmail.com>
