title: extjs grid summary row, got concated Strings
body: <p>I am trying to get the summary of a column,
  followed an example, summary row is there,
  but the cell values are concatenated Strings...</p>
  
  <p>For example, with cell values in a column "6","0","0"
  i get "600" in the summary.</p>
  
  <p>In grid declaration i put</p>
  
  <pre><code>features: {ftype: 'summary'}
  </code></pre>
  
  <p>and in column declaration:</p>
  
  <pre><code>summaryType: 'sum'
  </code></pre>
  
  <p>I know that javascript handles values as a String,
  i tried embracing it with parseInt(value)</p>
  
  <pre><code>summaryRenderer: function (value, summaryData, dataIndex) {
      return parseInt(value);
  }
  </code></pre>
  
  <p>but no effect, what i am doing wrong?</p>
  
  <p>(strangely, In the examples, it works without parseInt)</p>