The change ed0e6a9c11af replaced os.fork() with subprocess to try to fix race conditions in test_eintr (the test sometimes hangs on FreeBSD buildbots). os.fork() is not available on Windows, so this change should help to port test_eintr to Windows.

About win32-sleep-test.diff: I'm not sure that it's a good idea to introduce a new thread in test_eintr. Signal handlers is more complex when we have multiple threads. Would it be possible to spawn a new process which will send a signal every N seconds to its parent?