anchor.diff:  /// Sets all files in the directory readonly 
   let SetReadOnly readOnly (files: string seq) =
       files
  -    |> doParallel (fun file ->
  +    |> Seq.iter (fun file ->
           let fi = fileInfo file
           if fi.Exists then 
               fi.IsReadOnly <- readOnly
  
positive.code:     let cache = directoryInfo cacheDir
      if not cache.Exists then cache.Create()
      files
          |> doParallel (fun fileName -> 
              let fi = fileInfo fileName
              let cached = cacheDir @@ fi.Name
              let cachedFi = fileInfo cached
  
negative.code:     CreateDir target
      Directory.GetFiles(source, "*.*", SearchOption.AllDirectories)
      |> Seq.filter filterFile
      |> Seq.iter (fun file -> 
          let fi = file |> replaceFirst source "" |> trimSeparator
          let newFile = target @@ fi
          logVerbosefn "%s => %s" file newFile
  