Fix a bug in libsvn_client, uncovered by work on WC-NG.
Fix a bug in libsvn_client, uncovered by work on WC-NG.

* subversion/libsvn_client/commit_util.c
  (harvest_committables): Make the code match the comments by ensuring that
    used_url is always set.  Add a note about WC-NG to the comment.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion