title: Total score for the facet in solr & sunspot
body: <p>After search each facet row has value and count of the hits. </p>
  
  <p>Is it somehow possible to get total score (sum) of all hits in the facet without firing new searches?</p>
  
  <p>let's consider the following scenario:</p>
  
  <p>Model</p>
  
  <pre><code>class Article &lt; ActiveRecord::Base
    belongs_to :category
    searchable do
      text :title
      integer :category_id, :references =&gt; Category
    end
  end
  </code></pre>
  
  <p>Controller's method</p>
  
  <pre><code>def search
    @search = Article.search do
      keywords params[:q]
      with(:category_id, params[:c].to_i) if params[:c].present?
      facet :category_id
      data_accessor_for(Article).include = :category
      paginate(:page =&gt; params[:page])
    end
  end
  </code></pre>
  
  <p>Haml view excerpt</p>
  
  <pre><code>- search.facet(:category_id).rows.each do |row|
    %li
      = link_to(row.instance.name, params.merge(:c =&gt; row.value).except(:page))
      %div.score= row.score
  </code></pre>
  
  <p>So I want to get total score of the facet that is a sum of scores of hits in this facet.</p>