A double-blind, randomized, multi-center study to investigate the endometrial safety of a continuous, combined, oral estrogen/progestin preparation (0.5 mg 17b-estradiol [E2] / 0.25 mg drospirenone [DRSP]) and to compare the bleeding pattern of subjects treated with 0.5 mg E2 / 0.25 mg DRSP with the bleeding pattern of subjects treated with 1.0 mg E2 / 0.5 mg norethisterone acetate (NETA) when used for hormone therapy (HT) for 1 year in post-menopausal women