def <<( str )
      path = Pathname( str )

      case
      when !path.exist?
        raise Errno::ENOENT, path.to_path
      when !path.directory?
        raise Errno::ENOTDIR, path.to_path
      else
        super path.expand_path
      end
    end
def <<( str )
      path = Pathname( str )

      case
      when !path.exist?
        raise Errno::ENOENT, path.to_path
      when !path.directory?
        raise Errno::ENOTDIR, path.to_path
      else
        super path.expand_path
      end
    end
Appends a path to this path set. If the path exists, it
 will be expanded. Raises Errno::ENOENT if the path
 does not exist. Raises Errno::ENOTDIR if the path
 is not a directory.