title: Received "ValueError: Found wrong number (0) of constraints for ..." during Django migration
body: <p>While using Django 1.7 migrations, I came across a migration that worked in development, but not in production:</p>
  
  <p><code>ValueError: Found wrong number (0) of constraints for table_name(a, b, c, d)</code></p>
  
  <p>This is caused by an <code>AlterUniqueTogether</code> rule:</p>
  
  <pre><code>   migrations.AlterUniqueTogether(
           name='table_name',
           unique_together=set([('a', 'b')]),
     )
  </code></pre>
  
  <p>Reading up on bugs and such in the Django bug DB it seems to be about the existing <code>unique_together</code> in the db not matching the migration history.  </p>
  
  <p>How can I work around this error and finish my migrations?</p>