[NNTP] LIST EXTENSIONS (again)

[Howard Swinehart]

From: "Mark Crispin" <MRC at CAC.Washington.EDU>
> The server must advertise both NNTPv2 and NNTPv3.  A server which just 
> advertises NNTPv3 is not OK to an NNTPv2 client.

This returns us to the original problem of identifying broken servers.

NNTPV2 was supposed to distinguish between Netscape Collabra (has LIST 
EXTENSIONS but wrongly advertises OVER) and a truly compliant server. 
Without NNTPV2 and without a version number, a client based on this proposal 
won't see a difference between a future incompatible NNTPVx server and 
Netscape Collabra because neither will return NNTPV2.

With the version number proposal, we can do this:

if version is 2
    it's compatible
if version is larger than 2
    it's incompatible
if LIST EXTENSIONS works but no NNTP version
    it's Netscape Collabra