title: makemigrations doesn't detect changes in model
body: <p>I'm using django 1.9.6. I recently deleted my migrations and ran <code>migrate --run-syncdb</code> and <code>makemigrations my_app</code>. Today I added a new field to one of my models:</p>
  
  <p><em>models.py:</em></p>
  
  <pre><code>value = models.PositiveSmallIntegerField(null=True)
  </code></pre>
  
  <p>I tried to migrate the changes, but <code>makemigrations</code> doesn't detect the change. It's just the development version, so I can resync (I don't have to preserve the data), but running <code>--run-syncdb</code> again doesn't detect it either.</p>
  
  <p>Why isn't this migrating?</p>