select directive does not react to ngMultiple value changes #1484

The select directive decides whether it is selecting a single or a multiple value only once at link time.
When ngMultiple to change this property at run time, the select directive needs to watch this and change its behaviour accordingly. Currently it does not.
This can be seen by looking at the model in the standard example in the ngMultiple documentation.

<div ng-app="">
  Check me check multiple: <input type="checkbox" ng-model="checked"><br/>
  <select id="select" ng-multiple="checked" ng-model="selected">
    <option>Misko</option>
    <option>Igor</option>
    <option>Vojta</option>
    <option>Di</option>
  </select>
    <pre>{{selected | json }}</pre>
</div>​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​

Ticking the checkbox changes the visual appearance of the select control to a multiple select but the model does not change to an array of selected items.