Content-Range in Nethttp.Header missing "bytes"

Hi,

set_content_range in nethttp.ml sets header of the form "Content-Range: 598-3135/3136", but it should set "Content-Range: bytes 598-3135/3136",
see http://tools.ietf.org/html/rfc7233#section-4.2

Interestingly the headers set by Nethttp.set_content_range worked fine with clients like curl/wget or even browsers.
Then I tried using my server as an APT http repository and it complained:
HTTP/1.1 206 Partial Content
Accept-Ranges: bytes
Content-Length: 2538
Content-Range: 598-3135/3136
Content-Type: binary/octet-stream
Date: Sun, 25 Jan 2015 09:51:26 GMT
ETag: "2015-01-23 10:19:24.611:0ad6cf8d3cfc5ebfc5983d6e8c626bc8"
Last-Modified: Fri, 23 Jan 2015 10:19:24 GMT
Server: libres3-0.9.beta-68-g137d4f1-dirty
x-amz-id-2: dm9sLXJlcG8AL2RlYmlhbi9kaXN0cy93aGVlenkvSW5SZWxlYXNlADE0MjIxNzk0ODYuNDE=
x-amz-request-id: libres3_d598fe779a57c81f28f25e1dd9802276_14711_1209_1422179483.37


400 URI Failure
URI: [...]
Message: The HTTP server sent an invalid Content-Range header


Testcase (make sure Nethttp can parse the header it generates):

$ cat >x.ml <<EOF
#use "topfind"
#require "netstring"
let test_bytes b =
  let  h = new Netmime.basic_mime_header [] in
  Nethttp.Header.set_content_range h b;
  let cr = h#field "Content-Range" in
(*  if String.length cr < 6 || String.sub cr 0 6 <> "bytes" then
    h#update_field "Content-Range" ("bytes " ^ cr);
  let cr = h#field "Content-Range" in*)
  prerr_endline cr;
  assert (Nethttp.Header.get_content_range h = b)

let () =
  test_bytes (`Bytes ((Some (42L, 1233L), Some 1234L)));
  test_bytes (`Bytes ((Some (42L, 1233L), None)));
  test_bytes (`Bytes (None, Some 1234L));
EOF
$ ocaml x.ml
42-1233/1234
Exception: Nethttp.Bad_header_field "Nethttp.get_content_range".

Best regards,
--Edwin

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