 Randomized, Double Blind, Placebo-Controlled, Single-Dose, Parallel-Group Study to Evaluate the Onset of Action of a Single Dose of Intranasal GW685698X Aqueous Nasal Spray 100 mcg in Adolescent and Adult Subjects 12 years of age With Seasonal Allergic Rhinitis Exposed to Ragweed Pollen in an Allergen Challenge Chamber 