At this point, SHA-256 support is experimental and some behavior may
change. To avoid surprising unsuspecting users, require a build flag,
ENABLE_SHA256, to allow use of a non-SHA-1 algorithm. Enable this flag
by default when the DEVELOPER make flag is set so that contributors can
test this case adequately.
Signed-off-by: Nbrian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>