title: Django's GeoJSON serializer not serializing all fields?
body: <p>I'm using Django 1.8, with GeoDjango and PostGIS. I am using <code>HttpResponse</code> to return some GeoJSON:</p>
  
  <pre><code>from django.http import HttpResponse, JsonResponse
  code = request.GET.get('q', '')
  results = PCT.objects.filter(Q(code__startswith=code) |
                                   Q(name__icontains=code))
  results = results.filter(org_type='CCG')
  for result in results:
      print result.code
  geo_field = 'boundary'
  fields = ('name', 'code', 'ons_code', 'org_type', 'boundary', )
  return HttpResponse(serialize('geojson', results,
                      geometry_field=geo_field, fields=fields),
                      content_type='application/json')
  </code></pre>
  
  <p>In the console this prints a <code>code</code> field just fine:</p>
  
  <pre><code>99N
  </code></pre>
  
  <p>But the GeoJSON returned does not have a <code>properties.code</code> field. It has a <code>properties.name</code>, <code>properties.org_type</code> and <code>properties.ons_code</code> field though. </p>
  
  <p><img src="https://i.stack.imgur.com/wosbC.png" alt="enter image description here"></p>
  
  <p>Why is this? Is <code>code</code> a reserved name perhaps? If so, how can I fix this?</p>