svntest: Add new APIs to support conflict generation.
svntest: Add new APIs to support conflict generation.

* subversion/tests/cmdline/svntest/actions.py
  (fill_file_with_lines): New function which fills a file with new
   numbered lines, either appending to the file, or replacing its
   contents.
  (inject_conflict_into_wc): New function which creates a conflict.
  (ignore_conflict_files_singleton_handler): New merge singleton
   handler which ignores the support files generated by a merge
   conflict.
  (inject_conflict_into_expected_state): New function which updates
   the expected disk and status trees for a conflict.
  (make_conflict_marker_text): New function which creates the text for
   a conflict marker.

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