Minor tweaks to symmetric merge.
Minor tweaks to symmetric merge.

* subversion/libsvn_client/merge.c
  (svn_client__symmetric_merge_t): Tweak comment.
  (find_symmetric_merge): Add a minimal doc string.
  (svn_client__find_symmetric_merge): Remove unwanted comments.
  (do_symmetric_merge_locked): Remove unwanted comments. Add a
    TODO comment. Pass real instead of dummy depth, ignore_ancestry,
    force and record_only parameters.

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