title: Django admin inline calculated field won't save
body: <p>One of the fields in my inline needs to be calculated. I overrode the BaseInLineFormSet clean method and can do the calculation there and apparently set the field's value there but it doesn't get saved to the DB, and consequently is also not displayed. The field defaults to zero, btw, in case that matters. Here's a hard-coded version:</p>
  
  <pre><code>class EmployeeAssignmentInLineFormSet(BaseInlineFormSet):
      def clean(self):
          super(EmployeeAssignmentInLineFormSet, self).clean()
          self.cleaned_data[0]['cost'] = 5000
  </code></pre>
  
  <p>I also tried overriding save_formset in the ModelAdmin - same result:</p>
  
  <pre><code>def save_formset(self, request, form, formset, change):
      formset.cleaned_data[0]['cost'] = 5000
      formset.save()
  </code></pre>
  
  <p>When I set the value just in clean I can see it's been set when it gets to save_formset, but it still ends up being zero in the DB. Am I in the wrong place or what?</p>