title: Django clean removes an input field
body: <p>I keep getting a key error when trying to access the 'email_password' part of the post data.  At some point cleaned_data produces a dictionary without 'email_password' in it.  How do I solve this?</p>
  
  <pre><code>class EmailForm(forms.Form):
      email = forms.EmailField(required=True)
      pword = forms.CharField(
          label=_('Old Password'),
          required=True,
          widget=forms.PasswordInput,
      )
  
      def __init__(self, *args, **kwargs):
          request = kwargs.pop('request', None)
          self.user = request.user
          return super(EmailForm, self).__init__(*args, **kwargs)
  
      def clean(self, *args, **kwargs):
          cleaned_data = super(EmailForm, self).clean()
          data = cleaned_data['email']
          pword = cleaned_data['email_password']
          try:
              User.objects.exclude(id=self.user.id).get(email=data)
          except User.DoesNotExist:
              return cleaned_data
          else:
              raise forms.ValidationError(_("Email is already been used by another user"))
  </code></pre>