title: Update storyboard constraint using code
body: <p>I have a <code>UIImage</code> in code that I would like to enlarge vertically when a button is pressed. The <code>UIImage</code> is fully constrained in the storyboard and I would like to change its height when the button is pressed.</p>
  
  <p>I have linked the <code>UIImage</code> and its height constraint in the code:</p>
  
  <pre><code>    @IBOutlet weak var botBotCons: NSLayoutConstraint!
      @IBOutlet weak var botBot: UIImageView!
  </code></pre>
  
  <p>Then </p>
  
  <pre><code>@IBAction func testButton(sender: UIBarButtonItem) {
      println("testButton pressed")
      self.botBotCons.constant = 68   //or +=62 as its current constant is 6
      self.view.layoutIfNeeded()
  }
  </code></pre>
  
  <p>I get the <strong>testButton pressed</strong> message in the console, but the image doesn't resize. What am I doing wrong? Do I need to change something in the storyboard as well?</p>