title: KVO: How to get old / new values in observeValue(forKeyPath:...) in Swift?
body: <p>I have created an observer with <code>.Old | .New</code> options. In the handler method I try to fetch before after values, but compiler complains: <em>'NSString' is not convertible to 'NSDictionaryIndex: NSObject, AnyObject</em></p>
  
  <pre><code>override func observeValueForKeyPath(keyPath: String!, ofObject object: AnyObject!, change: [NSObject : AnyObject]!, context: UnsafeMutablePointer&lt;Void&gt;) {
  
      let approvedOld = change[NSKeyValueChangeOldKey] as Bool
      let approvedNew = change[NSKeyValueChangeNewKey] as Bool
  </code></pre>