title: Django Migration Missing ManyToManyField
body: <p>I've added a ManyToManyField to my app. Every restaurant can fall under many categories, and each category can be applied to many restaurants. The app has been working and running, and my models look like this:</p>
  
  <pre><code>class Category(models.Model):
      class Meta:
          verbose_name_plural = "categories"
  
      title = models.CharField(max_length=100)
  
      def __unicode__(self):
          return self.title
  
  class RestaurantInfo(models.Model):
      name = models.CharField(max_length=100)
      aboutUs = models.TextField(max_length=10000)
      founded = models.DateField()
  
      categories = models.ManyToManyField(Category)
  
      def __unicode__(self):
          return self.name
  </code></pre>
  
  <p>The ManyToManyFied is what is new. However, make migrations finds no changes to make.</p>