a value that is relative to the cur_flist object.  This makes the
variable consistent with how the sender and the receiver use it.

over-the-wire value, making it consistent with the ndx arg that
is passed to decrement_active_files().

in incremental recurse mode -- it is enough to check for them
when changing from one file-list to another.

flist_for_ndx() routine needs to work when cur_flist is NULL.

- Changed increment_active_files() to call check_for_finished_files()
  and to avoid calling both io_flush() and read_msg_fd() in the same
  iteration of a loop (since the former may have called the latter).

sends, and finished hard-links into check_for_finished_files(), a new
function that takes the place of check_for_finished_hlinks().  This
lets us signal the sender more rapidly when a file-list is done (which
ensures that it sends us more work to do in a timely manner), and also
avoids two potential deadlocks in the old code.

  if the io_flush() call happened to read the last message from the
  receiver, causing the read_msg_fd() call to deadlock.
- Fixed an error-looping problem when the server-side receiver failed
  to send a message down the error-msg pipe:  we no longer try to send
  a new error about this new failure down the same failing pipe.
- Make sure that we stop any deferring of forwarded messages in the
  generator when we are exiting with an error.

by the stats.total_read value so that the generator can set its value
to that of the receiver.  This makes log_exit() log the right value
when we're on the server side.

explicit that it is best used with an empty destination hierarchy.

  temporarily set to -1.
- Got rid of the msg2genr message cache.

set to -1.

so that the delete code doesn't change the value.

the directory time, and reveal any lack of dir-time touch-up.

  is now called for all our touch-up needs.
- Fixed a problem with --delete-delay interfering with the
  directory-time touch-up in incremental mode.

  readfd() so that the buffer is never partially filled.
- Make sure that msg2genr_flush() does not flush any messages while
  the flist-forwarding is active.
- Changed io_flush() to honor its flush_it_all arg again.

delete-after.

fewer bytes when exchanging the file-list index values.

mode.

--delete default.

(since the reason I had separated it no longer exists).