code: func pjoin(elem ...string) string {
  	hadSlash := strings.HasSuffix(elem[len(elem)-1], slash)
  	joined := path.Join(elem...)
  	if hadSlash && !strings.HasSuffix(joined, slash) {
  		return joined + slash
  	}
  	return joined
  }
docs: // Like path.Join, but preserves one trailing slash if present.