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).

- F_UID() is now defined to return a uid_t value.
- F_GID() is now defined to return a gid_t value.

  implied directories is working.

  public functions.
- Made add_uid() and add_gid() return the name or NULL.

- Changed some function names to make them more consistent.

incremental-recursion mode.