Comment 6 for bug 1171157

Patch against branch 1.4. "client/dotNET/Rss.cs"

Commentary
 1. Delete _duration (/replace by _durationTotal). It can be read from _options.duration.
 2. Create _durationTotal to store whole life time, i.e. multiplied for Per-Item or not.
 3. Calculate _durationTotal after we've parsed the feed and know how many items we're displaying.
 4. Use _durationTotal when setting the timer.
Also
 5. Add comment that the boolean is reversed creating the HTML but that the JavaScript in the HTML reverses it back!
 6. Don't try to dispose WebClient if it was never created (feed cache was fresh).