anchor.diff:      let cache = directoryInfo cacheDir
       if not cache.Exists then cache.Create()
       files
  -        |> doParallel (fun fileName -> 
  +        |> Seq.map (fun fileName -> 
               let fi = fileInfo fileName
               let cached = cacheDir @@ fi.Name
               let cachedFi = fileInfo cached
  
positive.code:             file
              |> directoryInfo
              |> setDirectoryReadOnly readOnly)
      |> ignore
        
  /// Deletes a directory if it exists
  let DeleteDir path =   
  
negative.code:   
  let SilentCopy target files =
      files
      |> Seq.iter (fun file ->
              let fi = fileInfo file
              let targetName = target @@ fi.Name
              let targetFI = fileInfo targetName
  