title: Django REST Framework: integer fields default value not showing up in browseable API form
body: <p>Using django 1.6 and rest framework 2.3.13</p>
  
  <p>In model class:</p>
  
  <pre><code>class A(models.Model):
      some_name = models.PositiveSmallIntegerField(default=15)
  </code></pre>
  
  <p>In serilizer:</p>
  
  <pre><code>class ASerializer(ModelSerializer):
      class Meta:
          model = A
          fields = (  'some_name'  )
  </code></pre>
  
  <p>In view:</p>
  
  <pre><code>class AViewSet(viewsets.ModelViewSet):
  
      queryset = A.objects.all()
      serializer_class = ASerializer
  </code></pre>
  
  <p>But in the api form, it's showing as 0, any idea?</p>