Group RSS feed (Activity logs) slow and time out when they get big

Need to add paging of the results in XML . Some group, like the Khan academy can not show the feed(e.g.http://www.curriki.org/xwiki/bin/view/Groups/Feed?space=Group_ScienceTX%2DHS&xpage=plain). This is needed for an integration with Ingboo to subscribe to a group feed.

Also we need a way to read the feed for closed groups