bug#24530: tests: revamp multibyte-white-space test to be more permissive

[Jim Meyering]

grep's multibyte-white-space would too often fail.
Its failure was mainly a reflection on the system's poor locale
support, so this test did not give good signal on whether one would be
well-advised to install the resulting grep binary.

I've done this:

        tests: revamp multibyte-white-space test to be more permissive
        This test elicits too many failures. Whether a system has accurate
        unicode "whitespace" attributes should not influence whether grep's
        test suite passes.  In many cases, now you will see a warning that
        some multibyte characters do not pass whitespace-related tests, but
        this test no longer fails.  However, if you run this test on a modern
        enough system, it does require that \s and \S do work properly with
        most of the listed characters.
        * tests/multibyte-white-space: Confirm that Fedora 24's locale
        tables still declare those four Unicode code points *not* whitespace.
        Honor a new column telling how to handle failure.  Provide more
        information in each diagnostic.

With the attached patch, even on Fedora 24, we see new warnings like
this (before those characters were not even checked), and the test
passes as it did before:

 warning: \s failed to match \xe2\x80\x87 in the en_US.UTF-8 locale
 warning: \S mistakenly matched \xe2\x80\x87 in the en_US.UTF-8 locale
 warning: \s failed to match \xe2\x80\x8b in the en_US.UTF-8 locale
 warning: \S mistakenly matched \xe2\x80\x8b in the en_US.UTF-8 locale
 warning: \s failed to match \xe2\x80\xaf in the en_US.UTF-8 locale
 warning: \S mistakenly matched \xe2\x80\xaf in the en_US.UTF-8 locale

More importantly, on less modern systems, while this test would fail
before, now it will merely emit warnings like the above.

tests--revamp-multibyte-white-space.diff
Description: Binary data