Hi all.

I did three (In my eyes) enhancements in gnus-sum.el:

1) The menu including the gnus-summary-limit-to-* functions was called
"Mark Limit". This is most certainly not the name it is supposed to have
and if it is, I think it is not very telling. I therefor changed it to
"Limit to".

2) There is no predefined shortcut for gnus-article-show-raw-article. I
think the shortcut belongs in gnus-summary-article-map but as r and R
are already in use, I assigned the function to w, so A w in the summary
buffer no calls gnus-article-show-raw-article.

3) When you call gnus-summary-limit-to-age via /t or the menu, you can
only limit the summary to articles older than x days. The user is asked
for x and if he gives a negative value nothing happens. I changed this,
so when the user says -x the summary is limited to articles younger than
x days. (e.g. /t -2 did nothing before and now limits the summary to
articles from today and yesterday)

If you like those changes, could someone commit the following patch? 
(I've signed the papers)