work towards getting ContainerFS::rename() working.
 - add back createMetalink, transferCanonical
 - add guts of ContainerFileSystem::rename() --- not fully complete yet,
   have to link in transferCanonical()

XXX: need two new callback for the index:
      1.  callback on unlink so indexes with external data files can
          remove them on a LogicalFS::unlink op
      2.  callback on rename so indexes with external data is aware
          of the rename operation
will add these shortly