ietf-nntp MODE STREAM response

[Jim Calvin]

The current draft (draft-ietf-nntpext-imp-03.txt) lists the following 
responses for MODE STREAM:

1.2.1.	Responses

   203 Streaming is OK
   500 Command not understood

I propose a third response be added to the list:

   400 not accepting articles

This is reasonable response, for example, when the server disk is full. 
CHECK and TAKETHIS current permit a 400 response. By including the response 
to MODE STREAM, the peer could detect such a situation before having sent 
out a blizzard of CHECKs or TAKETHISs.

Jim