title: Django: filter by latest per distinct column
body: <p>Given this FruitBasket model,</p>
  
  <pre>
  class FruitBasket(Model):
      fruit = CharField(max_length=128)
      count = PositiveIntegerField()
  </pre>
  
  <p>And this sample data,</p>
  
  <pre>
  id      fruit        count
  -----   ----------   -----
  0       apple        10
  1       banana       20
  2       apple        5
  3       banana       30
  </pre>
  
  <p>I want a django query that returns the following items:</p>
  
  <p>[ (2, apple, 5), (3, banana, 30) ]</p>
  
  <p>Essentially, grabbing the "latest" row <em>per</em> fruit (I've simplified the timestamp to rowid in this example.)</p>