title: form.cleaned_data is ignoring initial values
body: <p>I have the following form code:</p>
  
  <pre><code>class DisplaySharerForm(forms.Form):
      ORDER_BY_CHOICES = (
          ('customer_sharer_identifier', 'customer_sharer_identifier'),
          ('action_count', 'action_count'),
          ('redirect_link', 'redirect_link'),
          ('enabled', 'enabled'),
          ('click_total', 'click_total')
      )
  
      DIRECTION = (
          ('DESC','DESC'),
          ('ASC', 'ASC')
      )
  
      #These are the sorting options.  By default it's set to order by the customer_sharer_identifiers, descending, beginning at page 1.
      order_by = forms.ChoiceField(choices=ORDER_BY_CHOICES, required=False,initial='customer_sharer_identifier')
      direction = forms.ChoiceField(choices=DIRECTION, required=False,initial='DESC')
      action_type_id = forms.IntegerField(required=False)
      page_number = forms.IntegerField(required=False,initial=1)
  </code></pre>
  
  <p>Here's what I get when I try to create a <code>DisplaySharerForm</code> using the initial values:</p>
  
  <pre><code>&gt;&gt;&gt; f = DisplaySharerForm({})
  &gt;&gt;&gt; f.is_valid()
  True
  &gt;&gt;&gt; f.cleaned_data
  {'action_type_id': None, 'direction': u'', 'page_number': None, 'order_by': u'', 'customer_sharer_identifier': None}
  </code></pre>
  
  <p>Why isn't <code>cleaned_data</code> being set to the initial values I provided and what can I do to fix it?</p>