#308: need to reserve "negotiate" as auth scheme name

Hi,

I've got a TODO to mark the authentication scheme name "negotiate" as 
reserved (in draft-ietf-httpbis-authscheme-registrations); see 
<http://trac.tools.ietf.org/wg/httpbis/trac/ticket/308>.

Thoughts:

- the registry doesn't have a "status" entry; should we add that (with 
what values)?

- if we keep the registry simple, what's the reference we would put in? 
A pointer to a new appendix in 
draft-ietf-httpbis-authscheme-registrations, noting that "negotiate" is 
reserved as a scheme name, but it's not a valid scheme as per our 
requirements?

- that being said, should there be an erratum on RFC 4559 pointing out 
the problems?

Best regards, Julian