asyncio_subprocess_watchdog.patch:

* add test_asyncio.watchdog.setup_watchdog(): use faulthandler.dump_traceback_later() to kill the process if it hangs more than 'timeout' seconds (do nothing if faulthandler is not present, eg. on other Python VMs than CPython)
* add SubprocessTestsMixin.debug_info(): return returncode, stdout, stderr
* use debug_info() on functions using subprocess may may hang

The patch should give more information on the child process if it hangs. I didn't see the test_asyncio hang on "AMD64 Snow Leop 3.x" recently. The hang is probably random :-/

I chose a default timeout of 5 minutes, it should be enough for the short tests of test_asyncio. You may set the timeout to 15 minutes if a buildbot is too slow. Or set the timeout to 1 minute if you prefer to not hang a buildbot too long.

I tested asyncio_subprocess_watchdog.patch manually with a shorter timeout and by adding time.sleep(60) in echo.py, echo2.py and echo3.py.