title: PlaceholderAdmin throws <lambda>() takes exactly 1 argument (2 given)
body: <p>I've wrote a plugin for django-cms which has it's own model with one PlaceholderField. When I add a PlaceholderAdmin for model admin I'm getting this on admin site:</p>
  
  <pre><code>Exception Type: TemplateSyntaxError
  Exception Value:    
  Caught TypeError while rendering: &lt;lambda&gt;() takes exactly 1 argument (2 given)
  Exception Location: &lt;blablapath&gt;/python2.6/site-packages/cms/forms/widgets.py in render, line 199
  </code></pre>
  
  <p>I've been searching for solution and found only some problems with django-cms example which would not run without uncommenting some path in urls.py so I guess it might be problem with urls, especially that I do some magic in my urls. The question is: what conditions should hold for django-cms url's to be valid? Any ideas? Any solutions? Anybody had this problem before?  </p>