complain and die.

it gets called before the transfer starts (thus ensuring that it
can write out un-tweaked values of preserver_[ug]id vars).

- Make use of the [u]int{16,32,64}_t types, if they're around.

we always use a hardlinked group-number now.

on the receiving side.  This allows us to always use a 32-bit number
to identify the hardlink clusters, even on a system where pointers
are 64-bits.  Also made changes to handle the use of F_ROOTDIR() and
F_DEPTH() instead of the old union that wasted space on the
receiving side when pointers are 64-bits.

- Use just the 32-bit numbers in the file_extras union.
- Re-ordered the items in the file_struct to avoid padding
  on systems with 64-bit pointers.
- Got rid of the "dir" union in the file_struct, making the
  two items into "extras": F_DEPTH() for the receiving side,
  and F_ROOTDIR() for the sending side.
- Added PTR_EXTRA_LEN define.
- Got rid of F_HL_IDEV() define.

the values will be computed separately for the sender and the
receiver.

- Added an easy way to run the tests using protocol 29.

extra values we put at the start of the file_struct.  Also, deal
with the extras variable no longer being in the file_struct.

Also, clean up the new items.

prepending extra values at the start of the file_struct.