FYI: switching to fts: du, chmod, chgrp, chmod

[Jim Meyering]

FYI, I've converted du, chmod, and chgrp to use fts to perform
directory traversals.  chmod should be joining them soon.
I've included the relevant NEWS entries below.

Also, since these changes are pretty fundamental, the next release
will be called 5.1.0.

Since none of the affected tools have significant test coverage,
I'd really appreciate it if a few people would give them a try before
the next release.  I think everyone would prefer to find/address
any problems before the release rather than after.

** New features

  chown and chgrp can now process hierarchies of virtually unlimited depth
  chown and chgrp now accept POSIX-mandated -L, -H, and -P options

  chmod accepts new options: --preserve-root, --no-preserve-root

  du can now process hierarchies of virtually unlimited depth.
  Before, du was limited by the user's stack size and it would get a
  stack overflow error (often a segmentation fault) when applied to
  a hierarchy of depth around 30,000 or larger.

  du works even when run from an inaccessible directory

  du -D now dereferences all symlinks specified on the command line,
  not just the ones that reference directories

  du now accepts -P (--no-dereference), for compatibility with du
  of NetBSD and for consistency with e.g., chown and chgrp

  du's -H option will soon have the meaning required by POSIX
  (--dereference-args, aka -D) rather then the current meaning of --si.
  Now, using -H elicits a warning to that effect.