Convert various uses of hardcoded 20- and 40-based numbers to use
the_hash_algo, along with direct calls to SHA-1. Adjust the names of
variables to refer to "hash" instead of "sha1".
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>