title: Angular2 update form control value
body: <p>I have a problem building  dynamic angular2 forms with controls and select boxes,
  for example this <a href="http://plnkr.co/edit/zS4tpXnUfmtxHuoPKDPB?p=preview">plunker</a>:</p>
  
  <pre><code>    &lt;select class="form-control" ngControl="power"&gt;
        &lt;option *ngFor="#p of powers" [value]="p"&gt;{{p}}&lt;/option&gt;
      &lt;/select&gt;
  </code></pre>
  
  <p>You can select a hero power, and the control will have the same value. But if you press <code>Change Powers</code>, the selected value would be null but the control value is still the old value. This is a serious problem I think as this is a source of a lot of bugs when the form shows one thing but in reality it will submit something different, is there some way to update the content of the control ? There is <code>updateValue()</code> but you have to manually set the value in all those cases.</p>
  
  <p>There is also a similar case when you update the selectbox options after the form building, it will show a selected value in the selectedbox, while the control value would be null, any ideas on how to deal with this ?</p>