title: Jquery validate plugin disabled attribute bug
body: <p>I have a set of html input:checkbox items. One of these items has <em>disabled</em> attribute.
  Expected behavior is that jquery validation plugin will ignore <em>input</em> with <em>disabled</em> attribute, but will process validation on other elements which are not disabled.</p>
  
  <pre><code>&lt;input type="checkbox" name="example[]" value="1" minlength="1" required="required" disabled="disabled" /&gt;
  &lt;input type="checkbox" name="example[]" value="2" minlength="1" required="required" /&gt;
  &lt;input type="checkbox" name="example[]" value="3" minlength="1" required="required" /&gt;
  </code></pre>
  
  <p>I've created a live example to demonstrate the behavior. <a href="http://jsfiddle.net/cVMBA/24/" rel="nofollow">http://jsfiddle.net/cVMBA/24/</a></p>
  
  <p>The expected behavior is that at least one checkbox is selected in this case. If not, then the error should appear.
  Although as I can see  the behavior is really strange. If you look in console you can see that at first <em>errorPlacement</em> function is fired and afterward <em>unhighlight</em> function fires. So the problem here is that error is not shown.</p>
  
  <p>When you remove attribute <em>disabled="disabled"</em> the plugin will work as expected.
  Any ideas, or maybe a hack to override this behavior?</p>