[bug-idutils] new option: --files0-from

[Jim Meyering]

Pedro J. Ruiz Lopez added this feature:

  ** New features

    mkid and xtokid accept a new option --files0-from=FILE, to make them
    process only the files named in FILE.  FILE must contain a list of
    NUL-terminated file names.

based on what coreutils did via du, sort, wc.
Thanks, Pedro!

Later, I realized that the tools needn't (and must not) read in
the entire list of names before beginning to process them,
so I adjusted things to match what had been fixed in coreutils.

I've just pushed all of that:
  http://git.savannah.gnu.org/cgit/idutils.git/