title: ExstJs Store callback proper error handling
body: <p>I want to receive a personalized error message when trying to load a store and my connection times out or the DB it's not accessible ... when I do an Ajax Request is very easy because I get "response" as a parameter either in success or failure ...</p>
  
  <pre><code>Ext.Ajax.request({
     url: 'ajax_demo/sample.json',
     success: function(response, opts) {
        var obj = Ext.decode(response.responseText);
        console.dir(obj);
     },
     failure: function(response, opts) {
        console.log('server-side failure with status code ' + response.status);
     }
  });
  </code></pre>
  
  <p>But I'm facing problems to do the same when trying to load a store, I've defined a callback function but I only receive records, operation and success. </p>
  
  <pre><code>store.load({
          callback : function(records, options, success) {
              if (!success) {
  
                // what can I do here to show personalized error sent from server
              }
          }
      });
  </code></pre>
  
  <p><strong>So, what is the proper way to handle a response like this to show it to the user?</strong></p>
  
  <pre><code>{"success": false, "msg": "SomeExceptionFromServer"}
  </code></pre>
  
  <p>Best regards</p>