Add support for running the python tests in parallel on Windows.
Add support for running the python tests in parallel on Windows.

* win-tests.py
  (global, _usage_exit):  add -p and --parallel parameters.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion