title: Ember component bind-attr className doesn't change
body: <p>I'm trying to do something very simple here and I couldn't make it work so far. It's probably me doing silly things.</p>
  
  <p>You click in the circle to turn on and off a post. You can see that the alert message is coming right, the parameter is being updated, however I can't make the className change.</p>
  
  <p>Here's the JS Bin: <a href="http://jsbin.com/tusimozo/1/edit" rel="nofollow">http://jsbin.com/tusimozo/1/edit</a></p>
  
  <pre><code>&lt;script type="text/x-handlebars" data-template-name="index"&gt;
    {{ group-list posts=model }}
  &lt;/script&gt;
  
  &lt;script type="text/x-handlebars" id="components/group-list"&gt;
    &lt;div class="row"&gt;
      &lt;table width="100%"&gt;
        &lt;thead&gt;
          &lt;tr&gt;
            &lt;th width="90"&gt;Status&lt;/th&gt;
            &lt;th align="left"&gt;Categories&lt;/th&gt;
          &lt;/tr&gt;
        &lt;/thead&gt;
        &lt;tbody&gt;
          {{# each item in posts}}
            {{list-item published=item.published title=item.title pubDate=item.pub_date}}
          {{/each}}
        &lt;/tbody&gt;
      &lt;/table&gt;
    &lt;/div&gt;
  &lt;/script&gt;
  
  &lt;script type="text/x-handlebars" id="components/list-item"&gt;
    &lt;tr&gt;
      &lt;td&gt;
        &lt;a href="#" {{bind-attr class=":post-status published:on:off"}} {{action "publish"}}&gt;&lt;/a&gt;
      &lt;/td&gt;
      &lt;td align="left"&gt;{{title}}&lt;/td&gt;
    &lt;/tr&gt;
  &lt;/script&gt;
  </code></pre>
  
  <p>app.js</p>
  
  <pre><code>App = Ember.Application.create();
  
  posts = [{
    title: "Items",
    published: true
  }, {
    title: "Boards",
    published: false
  }];
  
  App.IndexRoute = Ember.Route.extend({
    model: function() {
      return posts; 
    }
  });
  
  App.ListItemComponent = Ember.Component.extend({
    actions: {
      publish: function() {
        var publishStatus = this.get('published') ? false : true;
        this.set('published', publishStatus);
        alert(this.get('published') ? 'publish' : 'unpublish');
      }
    }
  });
  </code></pre>
  
  <p>What am I missing here?</p>
  
  <p>Cheers!</p>