anchor.diff:  let ``BindingTarget raises property changed`` () =
       use bt = new TestBindingTarget()
   
  -    let obs = PropertyChangedObserver()
  -    obs.Subscribe bt
  +    let obs = PropertyChangedObserver(bt)    
   
       let ibt = bt :> IBindingTarget
   
  
positive.code:     use bt = new TestBindingTarget()
  
      let value = Mutable.create 0
      let obs = PropertyChangedObserver()
      obs.Subscribe bt
  
      let ibt = bt :> IBindingTarget
  
  
negative.code:     use dynamicVm = new DesktopBindingTarget()
      dynamicVm.BindView "Test" v2
  
      let obs = PropertyChangedObserver(dynamicVm)    
      
      let props = TypeDescriptor.GetProperties(dynamicVm)
      let prop = props.Find("Test", false)
  