Returns a File or Folder object that reperesents if the entire
        fragment of this directory starting with `source_root` were copied
        to `target_root`.

        >>> Folder('/usr/local/hyde/stuff').get_mirror('/usr/tmp',
                                                source_root='/usr/local/hyde')
        Folder('/usr/tmp/stuff')

def get_mirror(self, target_root, source_root=None):
        """
        Returns a File or Folder object that reperesents if the entire
        fragment of this directory starting with `source_root` were copied
        to `target_root`.

        >>> Folder('/usr/local/hyde/stuff').get_mirror('/usr/tmp',
                                                source_root='/usr/local/hyde')
        Folder('/usr/tmp/stuff')
        """
        fragment = self.get_relative_path(
                        source_root if source_root else self.parent)
        return Folder(target_root).child(fragment)