Logged In: YES 
user_id=33168

I was just about to check this in, but then I ran into a
problem.  IPv6 may not be enabled, even if the constant
AF_INET6 exists.  The cleanest way I saw to address this in
the test was to add a has_ipv6 boolean constant to the
socket module.  Martin, do you think this is acceptable?

Attached is a complete patch which should be safe (based on
the discussion below), includes tests and doc changes.