ooops, add comment about crashing if we go out of existence still observed

Author: mattneub

bk1ch13p380kvo/ch13p355kvo/AppDelegate.swift

@@ -46,7 +46,8 @@ class AppDelegate : UIResponder, UIApplicationDelegate {
         let opts : NSKeyValueObservingOptions = .New | .Old
         objectA.addObserver(objectB, forKeyPath: "value", options: opts, context: &con)
         (objectA as MyClass1).value = true
-        // objectA.removeObserver(objectB, forKeyPath: "value")
+        // comment out next line if you wish to crash
+        objectA.removeObserver(objectB, forKeyPath: "value")
         objectA = nil
 
         return true