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.

where the basename exists without actually changing how the data
is organized.

on the sending side, and the support routines for the receiving side
that handle using a "group number" for each hard-link cluster rather
than having to manage a pool of dev+inode data. (For protocol 30)

routine to keep track of which item is the first one in a particular
hard-link cluster.  It then abbreviates the sending of any follow-on
items in the cluster, reducing transfer bytes.  It also omits the
sending of any dev+inode data to the receiver, saving even more xfer
bytes (since the receiver can associate the entries based on the the
group's index number that is sent when abbreviating an entry).

- Added XMIT_HLINK_FIRST define.
- Added struct idev_node.
- Added F_HL_GNUM() for protocol 30 (used in place of F_HL_IDEV()).

get from the receiver.

for a long-standing bug combinding -H with --compare-dest.

- Added BITS_SET() and BITS_SETnUNSET() defines.
- Got rid of unused HL_* defines.
- Got rid of no-longer-needed struct hlist.
- Changed F_HL_LIST() to F_HL_PREV().
- Added F_NOT_HLINK_FIRST() and F_NOT_HLINK_LAST().
- Got rid of WITH_HLINK and WITHOUT_HLINK.
- Got rid of the hlink_pool in the file list.

- Turned maybe_ATTRS_REPORT var into a global for use by hlink.c.

- Improved the function names.
- Improved a few variable names.
- Got rid of the "is a hard link" message in favor of the normal status
  messages for files (e.g. --itemize-changes indicates hard-links).
- Fixed a long-standing bug when combining -H with --compare-dest.
- Made sure that code compiles when hard-linking is not available.