Two minor Argument Clinic bugfixes: use the name of the class in the
docstring for __new__ and __init__, and always use "goto exit" instead of
returning "NULL" for failure to parse (as _new__ and __init__ return ints).
asyncio: Cleanup logging in BaseEventLoop._run_once()

logger.log() is now responsible to format the timeout. It might be faster if
the log is disabled for DEBUG level, but it's also more readable and fix
an issue with Python 2.6 in the Trollius project.