lib/Unicode/UCD.t: Add missing arg to failure sprintf

This wasn't spotted before because the test never failed.
t/uni/case.pl: Use calculated test count

This test file calculates the number of tests, but discards it in favor
of done_testing().  Since we've gone to the trouble of computing it, use
it.
t/uni/case.pl: Improve test names.

This is clearer as to what is being tested and the desired result.