title: Border radius being displayed in select2 input group with checkbox
body: <p>I've spent hours trying to get rid of the border radius on my select2 append checkbox. As of now the dropdown is displayed with a checkbox on the left. The problem is that there seems to be a border radius between the two input group elements, something similar to the <a href="https://cloud.githubusercontent.com/assets/2598704/4386822/e0b86d50-43d4-11e4-82d7-7f86fe4d27e8.png" rel="nofollow">image</a>. The solution proposed was adding the input-group select2-bootstrap-prepend class to the wrapper element which doesn't work for me.</p>
  
  <p>The html is as follows</p>
  
  <pre><code>&lt;div class="col-lg-3"&gt;
      &lt;div class="panel-body"&gt;
         &lt;b&gt;Region&lt;/b&gt;&lt;br&gt;
              &lt;div class="input-group select2-bootstrap-prepend"&gt;
                  &lt;span class="input-group-addon"&gt;
                      &lt;input type="checkbox" checked&gt;
                  &lt;/span&gt;
                  &lt;select id="select2-single-append" class=" region"&gt;
                  &lt;/select&gt;
              &lt;/div&gt;
      &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  
  
  <p>View the running example from <a href="https://jsfiddle.net/senior01/kLchxehz/2/" rel="nofollow">jsfiddle</a></p>