title: UIAlertController with Custom UITextField
body: <p>I'm trying to use a custom UITextField, more precisely AKMaskField( <a href="https://github.com/artemkrachulov/AKMaskField" rel="nofollow">here is AKMaskField project on GitHub</a> )</p>
  
  <p>But I had no luck, here is my code, a simple UIAlertController:</p>
  
  <pre><code> @IBAction func buttonClick(sender: AnyObject) {
  
      var alert = UIAlertController(title: "Vincular CPF", message: "Digite seu CPF para acumular mais pontos no seu programa de fidelidade (Somente números)", preferredStyle: UIAlertControllerStyle.Alert)
  
      alert.addTextFieldWithConfigurationHandler(textFieldConfig) //Line with error
      alert.addAction(UIAlertAction(title: "Cancelar", style: UIAlertActionStyle.Cancel, handler: handleCancelButton))
      alert.addAction(UIAlertAction(title: "Enviar", style: UIAlertActionStyle.Default, handler: {
              (UIAlertAction) in
              println("ok")
          }))
  
  
  
      self.presentViewController(alert, animated: true, completion: {
  
  
      })
  
  }
  
  func textFieldConfig(textField: AKMaskField){
      textField.mask = "{ddd}.{ddd}.{ddd}-{dd}"
      textField.maskTemplate = "x"
      textField.maskShowTemplate = true
  
      //textField.keyboardType = .NumberPad
      //textField.placeholder = "00000000000"
  }
  </code></pre>
  
  <p>Here is the error message:</p>
  
  <pre><code> Cannot invoke 'addTextFieldWithConfigurationHandler' with an argument list of type '((AKMaskField) -&gt; ())'
  </code></pre>
  
  <p>The error is pretty clear, and I tried everything to force a downcast to an UITextField but nothing seems to work.</p>
  
  <p>Anybody have any idea how can I accomplish this?</p>