Instead of using get_oid_hex and GIT_SHA1_HEXSZ, use parse_oid_hex to
avoid the need for a constant and simplify the code.
Additionally, fix some comments to refer to object IDs instead of SHA-1
and update a constant used to provide an allocation hint.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>