to avoid confusion with Greenlet's spawn() classmethod

disable test_notexistent, because it takes way too much on windows for some reason and doesn't test much

prevent bogus complains about libevent version mismatch due to invalid VERSION define in libevent's config.h on windows

- the error was only seen with libevent-2 but not with libevent-1.4

fix setup.py to compile with libevent-2 on windows. Thanks to Luigi Pugnetti for the original patch.

- Removed --static and --dynamic options

If a negative value is raised, then a deprecation warning is printed. The plan is to raise a ValueError in such case.

greentest/mysubprocess.py: add interrupt() method, make send_signal() not raise ValueError if signal not available and use taskkill on windows if otherwise killing does not work

use Event instead of switch()