title: .attr("disabled", "disabled") issue
body: <p>I have this function toggles the disabled attribute form a input field: </p>
  
  <pre><code>$('.someElement').click(function(){     
    if (someCondition) {
       console.log($target.prev('input')) // gives out the right object
       $target.toggleClass('open').prev('input').attr('disabled', 'disabled');
    }else{
       $target.toggleClass('open').prev('input').removeAttr('disabled'); //this works
    }
  })
  </code></pre>
  
  <p>the <code>removeAttr</code> works fine but when i need to add the disabled again it does just nothing. My console.log is triggered (and giving me back the right input field) so I'm sure that my if statement works. But when I inspect the DOM with firebug in firefox, the disabled attribute does not appear.</p>
  
  <p>can someone help me?</p>
  
  <p>PS: please don't focus on the function or the if statement itself, works fine its just that attr that does not work for disabled... </p>
  
  <p><em>edit</em>: its an input type="hidden" is it possible that disabled does not work on hidden fields?</p>