Socks V5 functionality

[jadestorm]

One of my PyAIM/PyICQ users submitted this code and it works like a charm.
Thought it might be nice to include in the main tree.  I only see Socks V4
support as it stands.  There are two files here, I'll attach the other one in a
second.  I imagine there's no good reason why the second (sockserror.py) file
couldn't be merged into socks5.py, but hey.  Daniel Chandran
(daniel.chandran@gmail.com) submitted this code.  I offer it to Twisted proper
with his blessing.  =)

[jadestorm]

Here's a quick example of using it; you'll note that there is a check for
whether socks is configured so that it's obvious what the difference between a
normal connection and a socks 5 based connection is:
        if self.socksProxyServer and self.socksProxyPort:
            c = protocol.ProxyClientCreator(reactor, serviceClasses[service],
self, cookie, d)
            c.connectSocks5Proxy(ip, 5190, self.socksProxyServer,
int(self.socksProxyPort), "BOSCONN").addCallback(addService)
        else:
            c = protocol.ClientCreator(reactor, serviceClasses[service], self,
cookie, d)
            c.connectTCP(ip, 5190).addCallback(addService)

[jknight]

This looks like a nice feature but it needs tests.

[khorn]

FYI, This looks like the same code from this email message: http://twistedmatrix.com/pipermail/twisted-python/2003-February/003057.html except split into two files.

Assuming it is, the original author was Dmitry Litovchenko.

[glyph]

This would need test coverage, and some kind of OK from Mr. Litovchenko if it were to be included.