FYI: test-related changes

[Jim Meyering]

FYI, I've been factoring and cleaning up tests, moving from
the mk-script-based framework to the Coreutils.pm-based ones.
One interesting side effect is that this is removing *thousands*
of files from the distribution tarball.  On the other hand, each
of the converted tests require Perl, but that's a small price...
some would even say it's a feature.

"tar tf" says the coreutils-6.10 tarball contained 3354 entries.
Currently, we're down to 2772.  In the end there will be less than 1000.
Here are the remaining tests/* directories:

  cd tests && for i in join pr sort tac tail test; do \
    n=$(find $i -type f|wc -l);printf "$n\t$i\n"; done| sort -nr
  627     pr
  531     test
  405     sort
  196     join
  132     tail
  75      tac