Duplicate articles (= articles with the same URL) get deleted by leech.

Especially if subscribing to aggregated feeds, duplicate articles might come in on different feeds (Think of a subscription to Planet Drupal and e.g. Drie's blog.) In this case it would be desirable to make this fact available to the user.

So, if a duplicate article comes in, we don't want to create a new node in any case. But, if this article comes in from a different feed than the one that is already in the system, we want to store this bit of information by adding an additional entry in leech_news_item linking the article to the recent feed, too.

This change has some wider implications on leech that still have to be figured out. There is a special way leech_news attaches its data to nodes, links to node views etc.