title: Can't disable bootstrap button after complete
body: <p>It's pretty simple:  after calling bootstrap button('complete') on an element el,  </p>
  
  <pre><code>el.attr('disabled', 'disabled');​ 
  </code></pre>
  
  <p>and</p>
  
  <pre><code>el.addClass('disabled');​ 
  </code></pre>
  
  <p>have no effect</p>
  
  <p>Here is the jsfiddle <a href="http://jsfiddle.net/D2RLR/2732/" rel="nofollow">http://jsfiddle.net/D2RLR/2732/</a></p>
  
  <p>This is what I expect (jsfiddle of it working with 'loading'): <a href="http://jsfiddle.net/xgKZd/" rel="nofollow">http://jsfiddle.net/xgKZd/</a></p>