Comment 1 for bug 1744375

Might be able to enhance slo to accept some content-md5 query param -- have it

- automatically trigger the heartbeat=on behavior,
- move that value to sysmeta, so it won't get overwritten on POST,
- perform a GET immediately after the PUT,
- stream the bytes through a hasher (all the while continuing to
  dribble out bytes to the client), and
- report the result back in the final response.