Implement Feed Hierarchy

I'm torn on how we should implement this...

1. acts_as_tree (http://github.com/rails/acts_as_tree/tree/master/test/) doesn't take advantage of Rails 3 features like named scopes and it doesn't include any view helpers.
   
2. acts_as_category (http://github.com/bamnet/acts_as_category) (what we use for Flagship Docs) is super bloated. My branch includes some nice view helpers to generate trees but its still super bloated.
   
3. ancestry (http://github.com/stefankroes/ancestry) is an updated acts_as_tree with a few more features. It's not as bloated as acts_as_category, but it's creeping up there. I'm not sure how much I like their data-structure. Instead of a parent_id they store an entire parent tree id hierarchy.
   
4. better_nested_set (http://github.com/chris/better_nested_set) doesn't make a whole lot of sense to me because I don't think people will ever be manually assigning a sort order to their feeds.

My current feeling is we might be better off writing our own Rails 3 acts_as_tree plugin that keeps things very very simple (most of the work can be done with scopes now) but I'd like some input from everyone else before we move forward... thoughts?

(from [db889c3a67dacc3171548d5bf8e51c1821e566dd]) Implementing simple hierarchy in feed model. [#93 Implement Feed Hierarchy state:open responsible:"Brian Michalski"] http://github.com/wtg/concerto/commit/db889c3a67dacc3171548d5bf8e51...

(from [13d572fbdeb7e8d9b941dfb076e801ce6b8d9e7c]) Continuing work on [#93 Implement Feed Hierarchy], including support for current feed depth and sibling access. http://github.com/wtg/concerto/commit/13d572fbdeb7e8d9b941dfb076e80...