This variable is a "struct object_id", but uses the old-style name
"sha1". Let's call it oid to match more modern code (and make it clear
that it can handle any algorithm, since it uses parse_oid_hex()
properly).
Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>