title: Changing model doesn't affect ComboBox
body: <p>Suppose, we have the following code:</p>
  
  <pre class="lang-js prettyprint-override"><code>import QtQuick 2.4
  import QtQuick.Window 2.0
  import QtQuick.Controls 1.2
  import QtQuick.Layouts 1.1
  
  Window {
      id: win
      width: 800
      height: 600
  
      ListModel {
          id: listModel
          ListElement { name: "element1" }
          ListElement { name: "element2" }
          ListElement { name: "element3" }
      }
  
      ColumnLayout {
          anchors.centerIn: parent
          width: 200
          height: 200
          ComboBox {
              model: listModel
              currentIndex: 1
              Layout.fillWidth: true
          }
          ListView {
              model: listModel
              delegate: Text {
                      text: name
                  }
              Layout.fillHeight: true
              Layout.fillWidth: true
          }
          Button {
              text: "Change model"
              onClicked: {
                  listModel.get(1).name = "changed text";
                  //listModel.setProperty(1,"name","changed text"); this line not works too
              }
          }
      }
  }
  </code></pre>
  
  <p>So clicking the button have to change model's element with index 1. But changing the model affects only <code>ListView</code>. The <code>ComboBox</code> remains unchanged.
  Why that happens? Is it bug or feature? Is there a way to update <code>ComboBox</code> after changing its model?</p>