title: select2 will not disable or clear
body: <p>I have a secondary select slaved to a primary select (pick a store, then pick a department - identical to pick a country, then pick a state).</p>
  
  <p>I absolutely cannot get select2's ('enable',false) and ('data', null) methods to work, no matter how much other code I tear out.</p>
  
  <pre><code>&lt;select id="stores"&gt;
    &lt;option value="foo"&gt;foo&lt;/option&gt;
  &lt;/select&gt;
  &lt;select id="depts"&gt;
    &lt;option value="bar"&gt;bar&lt;/option&gt;
  &lt;/select&gt;
  
  // ...some logic that selects a store, then fetches that store's depts ...
  
  $('#depts').select2('enable',false);// does not disable control
  $('#depts').select2('data',null); // does not clear control
  </code></pre>
  
  <p>So I'm forced to do this:</p>
  
  <pre><code>$('select#depts').empty(); // clears HTML element
  $('#depts').select2(); // re-enhances select w/ select2
  $('#depts').select2('disable',true); // disables 
  </code></pre>
  
  <p>It behaves itself in jsfiddle, so I can't even post an example and request help. I'm just ... stumped.</p>