- Changed hlink_list[] to store file-list indexes instead of

- Changed hlink_list[] to store file-list indexes instead of
  pointers.
- Made hard_link_one() non-static so that the generator can call it.
  Improved it to do itemized output.
- Replaced do_hard_links() with hard_link_cluster(), which changes
  the hard-linking from a post-transfer loop into a per-cluster
  operation that occurs incrementally as the transfer updates (or
  finds unchanged) one item in the cluster.