the url to dictate arbitrary static method calls.
* Each xxx_rss helper has a single feed() call which takes an id as the argument
* xxx_rss::available_feedS() only returns feeds when they're applicable (ie
if you're viewing a tag, it won't show you an item feed).
* Feed urls are now in the module/feed_id form so that we can bind a
feed id to a given module
* Tightened up the Rss_Controller by using url::merge and some other tricks.
* Made the slideshow module express its own feed.
url to rss/feed/<feed name>/[<id>]
Where feed name is the name of the feed (i.e. albums, updates, comments, tags
etc.) and id is the optional element id that the feed applies to.
2) Protect the fullsize image with a permission check
3) Added a content:encoded element to each item which allows the image to show up in the body of the feed.
