dedup-{format,sift}.c: Find ways to save space by making hardlinks.

dedup-{format,sift}.c: Find ways to save space by making hardlinks.

Currently a bit work-in-progress.

  * dedup-format.c reads fshash files and reformats them a little, most
    importantly by adding the volume label from the fshash file to each
    line.

  * dedup-sift.c reads a sorted stream of dedup-formatted records and
    (currently) writes a report about which additional hardlinks can be
    made.  The tool is very careful not to corrupt the existing hardlink
    structure in a single volume, and not to hardlink files which are
    actually different, even if the fshash records are misleading.

Documentation is needed before these are ready for prime time.