code: public ProcessExecutor redirectErrorAlsoTo(OutputStream output) {
      streams(redirectErrorAlsoTo(pumps(), output));
      redirectErrorStream(false);
      return this;
    }
docs: Redirects the process' error stream also to a given output stream.
  This method can be used to redirect error to multiple streams.
  <p>
  Calling this method automatically disables merging the process error stream to its output stream.
  </p>
  
  @param output the output stream to redirect the error stream to
  @return This process executor.