[Twisted-web] Negotiate/Kerberos Auth

[Phil Mayers]

Interested parties might want to look at and comment on:

http://twistedmatrix.com/trac/ticket/3532
http://twistedmatrix.com/trac/ticket/3530

...the former being a "native" Negotiate auth method, the latter being a 
discussion of X-Remote-User and apache mod_auth_kerb.

The code in there is very much "todo", but we use both method and 
Twisted Web extensively, so I'll put some work into it over the next few 
days.