bundle: detect hash algorithm when reading refs

bundle: detect hash algorithm when reading refs

Much like with the dumb HTTP transport, there isn't a way to explicitly
specify the hash algorithm when dealing with a bundle, so detect the
algorithm based on the length of the object IDs in the prerequisites and
ref advertisements.

Signed-off-by: brian m. carlson <redacted>
Signed-off-by: Junio C Hamano <redacted>