Issue2406

Testing jython 2.7 vs python 2.7 on the same host.

Python 2.7:
>>> import socket
>>> s = socket.socket(socket.AF_INET6, socket.SOCK_STREAM)
>>> s.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, 0)
>>> s.bind(("localhost", 7171))
>>> s.listen(5)
>>> quit()


Jython 2.7:
>>> import socket
>>> s = socket.socket(socket.AF_INET6, socket.SOCK_STREAM)
>>> s.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, 0)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'IPV6_V6ONLY'

This is a serious deficiency that makes it difficult to implement dual-stack IPv4/IPv6 support.

Need to determine equivalent setting for Netty 4; unfortunately it's not as simple as setting ChannelConfig with a given ChannelOption (http://netty.io/4.0/api/io/netty/channel/ChannelOption.html)

Perhaps resolvable by modifying the support in _socket._get_jsockaddr2; and binding multiple addresses to a socket in _socket._realsocket.bind

Impacts Tornado support: #2458