'py3lint' make target added

This allows to run pylint via python3 on Python 3 code.
Trailing white-space removed
Catch IOError raised by getaddrinfo()

getaddrinfo sometimes raises random IOError exceptions when
a name cannot be resolved (Python or stdlib bug?). Catch it like
the 'socket.gaierror' exceptions.

This fixes the TestDumbBlockingResolver test for me.
README: added warning about current code status