title: Get Django Form Widget 'SelectDateWidget' to display 'Blank' option
body: <p>No documentation on this one, should be simple, but not functioning for me.</p>
  
  <p>Here's the raw code: <a href="http://code.djangoproject.com/browser/django/trunk/django/forms/extras/widgets.py" rel="nofollow noreferrer">http://code.djangoproject.com/browser/django/trunk/django/forms/extras/widgets.py</a></p>
  
  <p>Trying to pass a value of required=False to the Widget to get blank values (line 23 in the raw code:     none_value = (0, '---')) but get an unexpected argument raised with the code:</p>
  
  <pre><code>partner_date_of_birth = forms.DateField(required=False, 
              widget=forms.extras.SelectDateWidget(required=False,years=range(1940, 1992)))
  </code></pre>
  
  <p>Works without the second required=False argument, but doesn't have the 'Blank option in the form option list - which I'd need to be default.</p>
  
  <p>Any tips on where I'm going wrong?</p>