Tweak the test so that it does not depend on the platform using ".utf8" as
the extension signifying that a locale uses UTF8 encoding.  For the most
part this just requires using the abbreviated collation names "en_US" etc,
though I had to work a bit harder on the collation creation tests.

This opens the door to using the test on platforms that spell locales
differently, for example ".utf-8" or ".UTF-8".  Also, the test is now
somewhat useful with server encodings other than UTF8; though depending on
which encoding is selected, different subsets of it will fail for lack of
character set support.