title: Create composite index from a Django model
body: <p>I have the following model:</p>
  
  <pre><code>from django.db import models
  
  class PopulationData(models.Model):
      slot = models.IntegerField(db_index=True)
      sample = models.IntegerField()
      value = models.FloatField()
  
      class Meta:
          unique_together = (('slot', 'sample'),)
  </code></pre>
  
  <p>And I would like to create also a compound index on the column pair that have the <code>UNIQUE</code> constraint, like so:</p>
  
  <pre class="lang-sql prettyprint-override"><code>CREATE INDEX my_compound_index ON myapp_populationdata (slot, sample);
  </code></pre>
  
  <p>Right now I have a separate code connected to the <code>post_syncdb</code> signal that issues the previous SQL statement.  Is there any way to indicate it from the model specification?  (Note: I'm using the 1.3 branch).</p>