The RSS view is already defined in CMFPlone: `browser/syndication/templates/RSS.pt` and `rss.xml.pt`.  In p.a.contenttypes we used to override this for the Collection type (though in our case the RSS view was using rss.pt.xml). With this pull request we remove this.

Instead, in `behaviors/collection.py` we define an adapter to provide IFeed for collections and other types that have the new collection behavior. This gets used in the rss views in CMFPlone and all seems well.

Except that there is now a related error when I run the p.a.contenttypes tests on Plone 4.3. Need to look into that. Ah, that is because Documents have no primary field, which means turning them into an IFeedItem does not work. I will change the Document model schema for that. I don't know why that does not fail on Plone 5.