Python GSSAPI bindings

So, after a few blind alleys, I finally got the JWChat code working. Unfortunately, what this revealed is that the state of GSSAPI support for Python isn't that great.

Esentially, there are two different sources of GSSAPI-Python bindings:

• PyGSSAPI (on Sourceforge). This is old, and unmaintained. It's written in SWIG, but the SWIG source won't compile in recent SWIGs, and the provided C source won't work with current Python
  
• PyKerberos (part of Apple's CalDav server). This is a simple solution, but only provides access to an interface designed to do Negotiate-Auth. The interface isn't object oriented, nor will it garbage collect properly.
  

In order to get PunJab doing what I needed, the quickest route seemed to be to add SASL support to the PyKerberos library, so I did so. This solution isn't particularly clean, nor does it interface well with situations where you're trying to do anything other than perform a SASL handshake using credentials acquired in a previous NegotiateAuth transaction.

Other local projects required a way to do normal GSSAPI SASL from Python, and I really wanted to tidy up the PunJab code,so I ended up breaking and implementing my own Python bindings. Whilst not yet complete, these currently provide enough functionality to implement a GSSAPI SASL layer for the Twisted Jabber library, which solves our immediate local issue.

Once I've finished documenting the library, I'll package it up and announce it more widely.