anchor.diff:  
       Assert.True <| File.Exists ("cptgt" </> "a" </> "samplefile")
   
  -(*
   [<Test>]
   let ``copies fileset flatten``() =
       "." </> ".xake" |> File.Delete
  
positive.code:     }
  
      Assert.True <| File.Exists ("cptgt" </> "cpin" </> "a" </> "samplefile")
  *)
  
  [<Test>]
  let ``copies fileset NO flatten``() =
  
negative.code:     }
  
      Assert.True <| File.Exists ("cptgt" </> "samplefile")
  