A Randomized, Double-Blind, Double-Dummy, Placebo-Controlled, Crossover Study to Evaluate the Efficacy of TREXIMET (Sumatriptan + Naproxen Sodium) versus Butalbital-Containing Combination Medications (BCM) for the Acute Treatment of Migraine When Administered During the Moderate-Severe Pain Phase of the Migraine, GlaxoSmithKline.