Fix regression tests to work with REGRESS_OPTS=--no-locale

Hi all,

While doing some tests with the tree, I have noticed that we don't do
in the tests of unaccent the business that we have elsewhere
(test_regex, fuzzystrmatch, now hstore, collation tests, etc.) to make
the tests portable when these tests include UTF-8 characters but the
regression database cannot support that.

It took some time to notice that, which makes me wonder how relevant
this stuff is these days..  Anyway, I would like to do like the others
and fix it, so I am proposing the attached.

Thoughts?
--
Michael