- The sending side now sets the parent_ndx value in each file list.

- Leave a 1-entry gap between incremental file lists so that we can use
  that index value to refer to the parent directory of each file list.
- Set and use the new ndx_end value in the file list.  The incremental
  recursion mode omits dirs in this value (except in the first list)
  since the generator will be using the new "gap" ndx value to process
  each parent dir.