In libsvn_ra_serf, replace the pause handling for the update response that was
embedded through the old -not transition based- xml parser with a pause
handling response handler wrapper directly in the update logic.

* subversion/libsvn_ra_serf/eagain_bucket.c
  New file.

* subversion/libsvn_ra_serf/ra_serf.h
  (svn_ra_serf__create_bucket_with_eagain): New function.

* subversion/libsvn_ra_serf/update.c
  (SPILLBUF_BLOCKSIZE,
   SPILLBUF_MAXBUFFSIZE,
   PARSE_CHUNK_SIZE): New defines.
  (fetch_file): Remove old pause handling.
  (end_report): Remove old pause handling.
  (update_delay_baton_t): New struct.
  (update_delay_handler): New function.
  (finish_report): Wrap xml handler with delay handling. Process remaining
    data if any.

* subversion/libsvn_ra_serf/util.c
  (inject_to_parser): Remove unused argument.
  (svn_ra_serf__process_pending): Update caller.
  (svn_ra_serf__handle_xml_parser): Don't fetch status line. Is unused and
    requires the response to be a response bucket, which is not always the
    case any more.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1555774 13f79535-47bb-0310-9956-ffa450edef68