title: The correct way to override an initializer in Swift 1.1
body: <p>This used to work in Xcode 6.1 beta:</p>
  
  <pre><code>class MainViewController: NSViewController {
    convenience override init() {
      self.init(nibName: "MainView", bundle: nil)
    }
  }
  </code></pre>
  
  <p>After I switch to 6.1 GM2, it doesn't compile. Looks like the issue is related to "<a href="https://developer.apple.com/library/prerelease/mac/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/doc/uid/TP40014097-CH34-XID_683">failable initializers</a>" introduced in Swift 1.1. I've tried <code>convenience override init?()</code>, <code>convenience init?()</code> and <code>override init?()</code>, neither worked.</p>
  
  <p>So what's the correct way to override this kind of initializers as of today?</p>