title: How to get responsecode from store callback?
body: <p>I'm trying to handle session timeout server-side.
  When getting session timeout, my server sends back a response with json
  <code>{success: false}, ContentType: 'application/json', ResponseNo: 408</code></p>
  
  <p>store:</p>
  
  <pre><code>var storeAssets = Ext.create('Ext.data.Store', {
    model : 'modCombo',
    autoLoad : false,
    proxy : { limitParam : undefined,
      startParam : undefined,
      paramName : undefined,
      pageParam : undefined,
      noCache : false,
      type : 'ajax',
      url : '/caricaAssets.json',
      reader : { root : 'data' }
    }
  });
  </code></pre>
  
  <p>And on the client side, I handle callback loading store like this:</p>
  
  <pre><code>storeAssets.load({
    scope: this,
    callback: function(records, operation, success) {
      if (!success) { Ext.Msg.alert('Error'); }
    }
  });
  </code></pre>
  
  <p>To perform different responses, I'd like to change alert.
  So, if response no. is <code>408</code>, I can alert <code>session expired</code> (and so on, managing response numbers).</p>
  
  <p>But I didn't find any way to get response no. in store callback!</p>
  
  <p>Any suggestions?</p>