More changes according to review comments.


unittest/README.txt:
  Changes to manifest.
unittest/mysys/bitmap.t.c:
  Removed unused functions and variables. Marked unused parameters
  as unused. No need to test every size up to 4096 bits, testing to 1024,
  but I think this is too much as well.
unittest/unit.pl:
  Added test for version-specific function.