:through Associations don't respect default_scope

Consider the following case:

class Taggable < ActiveRecord::Base
  has_many :taggings
  has_many :tags, :through => :taggings
end

class Tagging < ActiveRecord::Base
  belongs_to :taggable
  belongs_to :tag

  default_scope :conditions => { :enabled => true }
end

class Tag < ActiveRecord::Base
  belongs_to :tagging
end

Tag.first.tags will entirely ignore the default_scope on Tagging.

I've included a patch which depends on other patch over at http://rails.lighthouseapp.com/p...