Fixed bug where System.out got closed in printHelp

- ArgumentParserImpl creates a PrintWriter upon printing help that wraps
  System.out, however, it also closes that PrintWriter before exiting the
  method, which in turn, closes System.out.  This meant that any calls to
  System.out.* by any other method would fail to get output.  See:
  http://stackoverflow.com/questions/8941298/system-out-closed-can-i-reopen-it
  for details of this problem.