title: UIButton doesn't listen to content mode setting?
body: <p>firstButton is a UIButton of type Custom. I'm programmatically putting three of them across each cell of a table, thusly:</p>
  
  <pre><code>[firstButton setImage:markImage forState:UIControlStateNormal];
  [firstButton setContentMode:UIViewContentModeScaleAspectFit];
  [cell.contentView addSubview:firstButton];
  </code></pre>
  
  <p>Elsewhere, I'm telling it to clipToBounds. What I get is a crop of the center square of the image, rather than an aspect-scaled rendering of it. I've tried this lots of ways, including setting the mode property on firstButton.imageView, which also doesn't seem to work.</p>