anchor.diff:  let ``calling Watch with new name adds a node`` () =
       let tree = new WatchTreeView()
       tree.Watch("w1", 1)
  +    
       test <@ tree.Nodes.Count = 1 @>
       test <@ tree.Nodes.Find("w1", false) <> null @>
   
  
positive.code:     let value = "hello"
      tree.Watch("w1", value)
      tree.Watch("w1", value)
      test <@ tree.Nodes.Count = 1 @>
      test <@ tree.Nodes.Find("w1", false).Length = 1 @>
      test <@ ((tree.Nodes.Find("w1", false).[0].Tag :?> Watch).RootInfo.Value :?> string) =& value @>
  
negative.code:     let tree = new WatchTreeView()
      tree.Watch("w1", 1)
      tree.Watch("w2", 2)
      
      test <@ tree.Nodes.Count = 2 @>
      test <@ tree.Nodes.Find("w1", false).Length = 1 @>
      test <@ tree.Nodes.Find("w2", false).Length = 1 @>
  