I am seeing this with `socket.AF_INET6` on Windows running python 2.7.14
```
[00:02:33]   File "C:\projects\pika\pika\adapters\host_tcp_connector.py", line 153, in _check_already_resolved
[00:02:33]     socket.inet_pton(socket.AF_INET6, 'localhost')
[00:02:33]   File "C:\Python27\lib\site-packages\twisted\python\compat.py", line 68, in inet_pton
[00:02:33]     raise ValueError("Illegal characters: %r" % (''.join(x),))
[00:02:33] ValueError: Illegal characters: 't'
```

With `socket.AF_INET`, `socket.inet_pton(socket.AF_INET, 'localhost')` raises `socket.error` as expected.

For comparison, with Python 2.7.10 running on OS X, both AF_INET and AF_INET6 raise `socket.error`.

This behavior goes against the socket documentation https://docs.python.org/2/library/socket.html which states "Supported values for address_family are currently AF_INET and AF_INET6. If the IP address string ip_string is invalid, *socket.error* will be raised."

Your traceback seems to include both pika and twisted, and as best I can tell, `socket.inet_pton` does not exist on Windows in Python 2.7.  If I've diagnosed this incorrectly, please reopen the ticket with a reproducer that does not depend on pika or twisted.

Zachary, thank you for noticing that Twisted is involved. inet_pton definitely exists on Windows 2.7.14, but it turns out that Twisted monkey-patches it if `socket.inet_pton(socket.AF_INET6, "::")` fails.

Aha! - but this suggests that Window's Python 2.7.14 implementation of `socket.inet_pton()` has a bug in that it fails to recognize '::' as the the IPv6 unspecified address 0:0:0:0:0:0:0:0, so `socket.inet_pton(socket.AF_INET6, "::")` fails. I wonder if this exists on Windows Python3 implementations?

Indeed, confirmed no `inet_pton()` on Windows in Python 2.7 :(.