title: Extjs Rollback model changes on store save failure
body: <p>I am using ext-js 4.0.7, and I am trying to find the way to rollback changes in model if saving failed.</p>
  
  <p>My store is </p>
  
  <pre><code>Ext.define('TEST.store.TestStore',{
      extend: 'Ext.data.Store',
      storeId: 'testStore',
      model: 'TEST.model.TestModel',
      autoLoad: false,
      proxy: {
          type: 'rest',
          url: 'some/api',
          reader: 'json'
      }
  });
  
  ...
  var me=this,
  testStore = me.getStore('TEST.store.TestStore');
  me.test = testStore.getAt(0);
  
  //here are I am changing it
  
  me.test.save({
  failure: function(record,operation) {
      console.log(test);
      test.reject();
      console.log(test);
  }
  });
  </code></pre>
  
  <p>But reject is not working. Is there any other way to clear this model?
  Thanks</p>