Item12027: Expand logger tests for site CharSet

And add test for log and playback of a unicode string.

This test fails for the Compatibility and Plainfile loggers when the
site CharSet is set to iso-8859-1.  Also the test is a bit noisy with
debug messages until it's fixed.

git-svn-id: http://svn.foswiki.org/trunk/UnitTestContrib@17219 0b4bb1d4-4e5a-0410-9cc4-b2b747904278