title: Under what circumstance would trigger `rowHasChanged` on ListView?
body: <p>I have create a <code>ListView</code> like this:</p>
  
  <pre class="lang-jsx prettyprint-override"><code>var data = [{id: 1, count: 1}, {id: 2, count: 1}];
  
  var ds = new ListView.DataSource({
      rowHasChanged: function (row1, row2) { 
         console.log('changed');
         return true;
      }
  });
  var ListViewExample = React.createClass({
      getInitialState: function () {
          return {
              dataSource: ds.cloneWithRows(data)
          }
      },    
      componentDidMount: function() {
          setTimeout(()=&gt;{
              console.log('changing...');
              data[0].count += 1;
              this.setState({
                  dataSource: ds.cloneWithRows(data)
              });
          },3000);
      },
      render: function() {
          console.log('render')
        return (
          &lt;ListView
            initialListSize={3}
            dataSource={this.state.dataSource}
            renderRow={(rowData) =&gt; &lt;Text&gt;{rowData.id}:{rowData.count}&lt;/Text&gt;}
          /&gt;
        );
      }
  });
  </code></pre>
  
  <p>Run this code and the log show:</p>
  
  <pre><code>[tid:com.facebook.React.JavaScript] 'Running application "mytest" with appParams: {"rootTag":1,"initialProps":{}}. __DEV__ === true, development-level warning are ON, performance optimizations are OFF'
  2015-08-03 20:40:10.385 [info][tid:com.facebook.React.JavaScript] 'render'
  2015-08-03 20:40:13.396 [info][tid:com.facebook.React.JavaScript] 'changing...'
  2015-08-03 20:40:13.398 [info][tid:com.facebook.React.JavaScript] 'render'
  </code></pre>
  
  <p>And when data is changed, the view was changed too. </p>
  
  <p>But why the <code>rowHasChanged</code> did not be triggered? (Never see the log <code>changed</code>)</p>