converted t/win32.t/system* to test.pl style
Corrections to 0511665b4b

- require './test.pl' in a BEGIN block, rather than use './test.pl'.
- Ensure the tests are done in the same program that emits the plan()
  otherwise one copy of test.pl thinks tests were planned but not done
  and the other thinks tests were done without being planned.
- Fix indentation.