title: Solr faceting: Inconsistent JSON formatting
body: <p>I have the following two fields in my solr schema:</p>
  
  <pre><code>&lt;field name="brand_id"     type="string" indexed="true" stored="true" /&gt;
  &lt;field name="category_id"  type="string" indexed="true" stored="true" /&gt;
  </code></pre>
  
  <p>When I make a request with facets enabled (faceting on brand_id)
  <a href="http://example.com/solr/select?wt=json&amp;facet=true&amp;facet.mincount=1&amp;facet.field=brand_id&amp;q=">http://example.com/solr/select?wt=json&amp;facet=true&amp;facet.mincount=1&amp;facet.field=brand_id&amp;q=</a>* :* </p>
  
  <p>faceting output is returned in object notation: </p>
  
  <pre><code>"facet_counts": {
      "facet_queries": { }
      "facet_fields": {
           "brand_id": [
              {"1350492":14},
              {"1350578":12},
              {"1350600":11},
              {"1350617":8}
          ]
      }
  }
  </code></pre>
  
  <p>However, repeating the same request using the 'category_id' as a facet field returns an array notation
  <a href="http://example.com/solr/select?wt=json&amp;facet=true&amp;facet.mincount=1&amp;facet.field=category_id&amp;q=">http://example.com/solr/select?wt=json&amp;facet=true&amp;facet.mincount=1&amp;facet.field=category_id&amp;q=</a>* :*</p>
  
  <pre><code>"facet_counts":{
      "facet_queries":{},
      "facet_fields":{
          "category_id":[
              "230",20,
              "259",13,
              "154",12,
              "249",11
          ]
      }
  }
  </code></pre>
  
  <p>Is there a way to force the object notation formatting? I am using Solr 3.6</p>
  
  <p><strong>-- UPDATE --</strong></p>
  
  <p>Using XML format returns correct results:</p>
  
  <pre><code>&lt;lst name="facet_counts"&gt;
  &lt;lst name="facet_queries"/&gt;
  &lt;lst name="facet_fields"&gt;
      &lt;lst name="brand_id"&gt;
          &lt;int name="269115"&gt;136&lt;/int&gt;
          &lt;int name="269394"&gt;110&lt;/int&gt;
      &lt;/lst&gt;
  
  
      &lt;lst name="category_id"&gt;
          &lt;int name="1348814"&gt;228&lt;/int&gt;
          &lt;int name="1350591"&gt;218&lt;/int&gt;
      &lt;/lst&gt;
  </code></pre>