[NNTP] Article Reinstatement

[Clive D.W. Feather]

>    The client may make use of the low water mark to
>    remove all remembered information about articles with lower numbers,
>    as these will never recur.

This was written like that so as to support the common behaviour of a
.newsrc file that contained lines like:

    uk.railway: 1-85623,85625,85629-85641

which listed the articles to be treated as read. If the server offers a
low-water mark of 85627, the client knows that 85624 and 85626 are *never*
going to get read and can change the line to:

    uk.railway: 1-85626,85629-85641

-- 
Clive D.W. Feather          | If you lie to the compiler,
Email: clive at davros.org     | it will get its revenge.
Web: http://www.davros.org  |   - Henry Spencer
Mobile: +44 7973 377646