ra_serf: Format distinguished names properly.

* subversion/libsvn_ra_serf/util.c
  (convert_organisation_to_str): Use only present fields for organisation 
   string.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1514804 13f79535-47bb-0310-9956-ffa450edef68