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".

alone to ensure that files inside a dir are fully protected.