ITEM_UPDATING bit) to make us compatible when sending/receiving bits
to/from an earlier pre-release.

ITEM_UPDATING bit) when ITEM_TRANSFER or ITEM_LOCAL_CHANGE is set.
This lets us interact compatibly when sending itemized bits to an
earlier pre-release.

This lets us be more compatible with the earlier pre-releases
with a better heuristic for backward-compatible itemized bits.

- Changed read_iflags() to read/write a suffixed hard-link name.

- Send MSG_SUCCESS for hard-linked files when -H was specified.

of the "the_file_list" global.

  updated locally instead of being updated remotely.
- Added support for outputting 'a' in the itemized log-output (for
  future use in extended-attribute handling).

- Added hlink_list, a FIFO list of finished hard-link items.
- Made get_redo_num() check for finished hard-link items and
  call the generator when they are found.  This ensures that
  we finish all the hard-link items by the time the MSG_DONE
  is read and returned to the generator.
- Added get_hlink_num() to read the new hlink_list.

  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.

  it non-static so the hard-link code can now output itemized
  messages.
- Made the locally-changed items (such as dirs and symlinks) itemize
  using a new ITEM_LOCAL_CHANGE flag instead of the (renamed)
  ITEM_TRANSFER flag (formerly ITEM_UPDATING).
- Improved the hard-link support by having a cluster of hard-linked
  files get processed as soon as we notice that a single item is
  already up-to-date, or it succssfully finishes being updated.
- The hard-linking that occurs when using --link-dest will now be
  mentioned at higher levels of verbosity IFF %i is in the log-
  format.

- Added defines ITEM_HARD_LINKED, ITEM_LOCAL_CHANGE,
  ITEM_REPORT_XATTRS, and SIGNIFICANT_ITEM_FLAGS.
- Changed the "next" var in struct hlink into an int.

new functions read_iflags() and maybe_log_item().

function called read_iflags() (which was made generic enough that
the receiver could use it too).  Also call the new maybe_log_item().

- Made log_formatted() and log_item() take an "hlink" arg that
  will be used to pass in a hard-link name for use in %L.

generic flist_num_{push,pop}() functions that can support other
folks caching off file-list index numbers.

having this code in generator.c and receiver.c.

  only needed back when the generator was reading a separate redo
  pipe from the message pipe.
- Fixed a potential data corruption in the data that the generator
  is sending:  if a message comes in from the receiver, we now make
  sure that we can't put the forwarding of this message to the sender
  into the middle of a multiplexed-write record that the generator
  is trying to flush.

- Got rid of test of read_batch in an am_sender section since
  there is never a sender process for --read-batch.

recv_generator() so that they don't trigger erroneously when
--link-dest is specified.

- If --compare-dest find a file that is not the same in attributes,
  we need to copy the file.

itemize() function.

copying a file that has an exact match in any of the dirs.

we need to re-stat() the file to restore "st".