A 4-Week, Multicenter, Randomized, Double-Blind, Placebo-Controlled Phase 3 Trial To Evaluate The Efficacy And Safety Of Saxagliptin In Comparison To Placebo As Add On Treatment To Metformin XR In Subjects With Type 2 Diabetes Who Have Inadequate Glycemic Control With Diet And Exercise And A Stable Dose Of Metformin ≥1500 mg/Day