'Updates symlinks to use archive_dir'

def _update_symlinks(self):

    for kind in ALL_FOUR:
        link = getattr(self, kind)
        previous_link = get_link_target(link)
        new_link = os.path.join(self.relative_archive_dir(link), os.path.basename(previous_link))
        os.unlink(link)
        os.symlink(new_link, link)
