title: render :json does not accept options
body: <p>I'd love to use <code>render :json</code> but it seems its not as flexible.  Whats the right way to do this?</p>
  
  <pre><code>respond_to do |format|
    format.html # index.html.erb
    format.xml  { render :xml =&gt; @things }
  
    #This is great
    format.json { render :text =&gt; @things.to_json(:include =&gt; :photos) }
  
    #This doesn't include photos
    format.json { render :json =&gt; @things, :include =&gt; :photos }
  end
  </code></pre>