[Twisted-Python] Integrating web.guard and web.twcgi

[Moshe Zadka]

OK, here's the deal. 
There's a Whole Lotta (TM) CGIs that use REMOTE_USER which the web
server is supposed to set if the user sent the apppropriate HTTP
authentication headers and the .htaccess (or whatever - in our case
the .cred database) matches. Specifically, that's how roundup
works. No, I'm not in the mood to integrate Roundup with Twisted,
thanks for asking.

So, any idea how to get web.twcgi to properly set REMOTE_USER based
on a parent's .guard? I'm drawing a blank here...
(perhaps a .guard should stamp the Request object as it is passing
it through...)