builtin/name-rev: convert to struct object_id
Convert all the uses of unsigned char [20] to struct object_id. Also,
convert some hard-coded integers into constants.
name_rev_line accepts a wide variety of free-form input and only
interprets 40-character hex values, passing through everything else.
Consequently, it is not a good candidate for parse_oid_hex, which is
much stricter.
This change is a prerequisite for converting parse_object.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>