Commits e07b331bf489 and b9de5e55f798 run wakeup and pending signal tests in a subprocess to avoid border effects with threads. It should make these tests more reliable, not only on FreeBSD 6.

PendingSignalsTests now use os.kill() instead of signal.pthread_kill() in most tests (except test_pthread_kill and test_pthread_kill_main_test). We don't need pthread_kill() here anymore because we know that we have exactly one thread. I prefer to use the simple and common os.kill(), and only use pthread_kill in pthread_kill tests.

I'm not proud of that, but I added a workaround for the kernel bug (create a dummy thread, just to initialize the pthread library) in test_pthread_kill(). I don't know how to write a (simple and) reliable test on FreeBSD 6 without this workaround. But I prefer to use a workaround than skipping the test.

I don't think that it would be revelant to use the workaround in test_pthread_kill_main_test(). I chose to skip the test on FreeBSD 6, even if the test was written for this OS (issue #12392).