title: Select2: How to unselect all options and select only one
body: <p>I’m using <code>Select2</code>, a great plugin.</p>
  <p>HTML:</p>
  <pre class="lang-html prettyprint-override"><code>&lt;select id=&quot;fruits&quot; multiple=&quot;true&quot;&gt;
    &lt;option value=''&gt;All
    &lt;option value='Apple'&gt;Apple
    &lt;option value='Pear'&gt;Pear
    ...
  </code></pre>
  <p>JavaScript:</p>
  <pre class="lang-js prettyprint-override"><code>$('#fruits').select2();
  </code></pre>
  <p>When I select the “All” option, I need to unselect all previously selected options and have only the “All” option selected.</p>
  <p>I’ve tried</p>
  <pre class="lang-js prettyprint-override"><code>onChange=&quot;$('#fruits').select2('val', ['All']);&quot;
  </code></pre>
  <p>as well as</p>
  <pre class="lang-js prettyprint-override"><code>onChange=&quot;$('#fruits').select2('data', ['All']);&quot;
  </code></pre>
  <p>but it does not seem to work for me.</p>
  <p>Any clues?</p>