Fix issue 1421.
Fix issue 1421.

* tools/cvs2svn/cvs2svn.py (RepositoryMirror.change_path): Add 
    only_if_already_exists parameter. Update docstring.
  (Dumper.prune_entries): Call change_path with only_if_already_exists set. 


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@847080 13f79535-47bb-0310-9956-ffa450edef68

wbond/subversion,wbond/subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,wbond/subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion