get_remote_heads: convert to struct object_id
get_remote_heads: convert to struct object_id

Replace an unsigned char array with struct object_id and express several
hard-coded constants in terms of GIT_SHA1_HEXSZ.

Signed-off-by: brian m. carlson <738bdd359be778fee9f0fc4e2934ad72f436ceda@crustytoothpaste.net>
Signed-off-by: Jeff King <696e3fbcf235d40b6ea1ebd61c87cbea79d444e7@peff.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git