fix bug where some pet states would also show many items on top of them

At first I thought this was an error in the data migration process when moving SWF assets
to having their own unique IDs, but then realized that the query for a pet state's SWFs
didn't include the (parent_type = 'Item') condition. Oops. Turns out, I only connected the
items to parent_swf_asset_relationships polymorphically. Pet states were still doing it the
hackish way. Set the pet states to use the lovely polymorphic relationship and we're good
to go.

app/models/pet_state.rb

@@ -3,7 +3,7 @@ class PetState < ActiveRecord::Base
   
   has_many :contributions, :as => :contributed # in case of duplicates being merged
   has_many :outfits
-  has_many :parent_swf_asset_relationships, :foreign_key => 'parent_id',
+  has_many :parent_swf_asset_relationships, :as => :parent,
     :autosave => false
   has_many :swf_assets, :through => :parent_swf_asset_relationships