Message 100420 - Python tracker

I experienced this hang with Linux AMD64.

It occurs in test_send_signal.
It is because signal.SIGINT is not always handled (see #3137).

As a workaround, there's 2 choices: add a delay between Popen and send_signal, or retry SIGINT 2 or 3 times.

Windows should not be affected, because it uses signal SIGTERM in the test.