A written agreement among the stockholders of a close corporation holding a majority of the outstanding stock entitled to vote, whether solely among themselves or with a party not a stockholder, is not invalid, as between the parties to the agreement, on the ground that it so relates to the conduct of the business and affairs of the corporation as to restrict or interfere with the discretion or powers of the board of directors. The effect of any such agreement shall be to relieve the directors and impose upon the stockholders who are parties to the agreement the liability for managerial acts or omissions which is imposed on directors, to the extent and so long as the discretion or powers of the board in its management of corporate affairs is controlled by such agreement.