A federal judge has cleared the way for three plaintiffs to challenge a policy limiting the number of books Cook County Jail inmates may possess. In a written opinion Wednesday, U.S. Magistrate Judge Maria G. Valdez rejected the argument that the plaintiffs — two former inmates and a woman who corresponds with current inmates — lack standing to seek a declaration that the policy is unconstitutional. The jail allows inmates to have only three books or magazines in their cells at a time. Valdez conceded …