Fixed issue #4233. Changed semantic of _fileio.FileIO's close() method on file objects with closefd=False. The file descriptor is still kept open but the file object behaves like a closed file. The FileIO object also got a new readonly attribute closefd. Approved by Barry Backport of r67106 from the py3k branch

char *getcwd(char *buf, int size)
{
  buf[0] = '\0';
  return buf;
}