forker.py:
    Extend start_zeo_server() on Windows with arg that specifies port,
    which is used to restart the server on the same port.

    Remove unnecessary imports.

    Set PYTHONPATH for the spawned script.

testZEO.py:
    Refactor ConnectionTests into abstract base class with two platform-
    specific subclasses.

    Add goofy test_suite() function, which is goofy because I can't figure
    out how to use unittest any other way.

winserver.py:
    Keep track of storage in ZEOTestServer so that its close() method can be
    called when the server exits.