Fix \xa0 matching both [\s] [\S], et.al.

Fix \xa0 matching both [\s] [\S], et.al.

This bug stemmed from Latin1 characters not matching any (non-complemented)
character class in /d semantics when the target string is no utf8; but having
unicode semantics when it isn't.  The solution here is to add a special flag.

There were several tests that relied on the broken behavior, specifically they
tested that \xff isn't a printable word character even in utf8.  I changed the
deparse test to instead use a non-printable code point, and I changed the ones
in re_tests to be TODOs, and will change them back using /a when that is
shortly added.