A 2-year, Multicenter, Open-label, Phase IIIb Extension Study to Assess Bone Mineral Density and Bone Turnover Response to 5 mg Daily Risedronate Treatment in Women with Postmenopausal Osteoporosis Who Sequentially Completed Clinical Studies RVE009093, RVE1996077, RVE1998080, and RVE2001079 (NCT01249261)