Oh, Danny boy, ’tis the time of year when Irish bagpipes are calling in the concrete glens of New York City. The annual parade — which bills itself as the world’s largest and oldest — drew throngs to Fifth Avenue to await bagpipes and bands, and give homage to Ireland’s patron saint. Veteran parade watchers arrived before dawn to claim space in the squares for picnic tables and party tents. Bars opened at 7 a.m. to greet customers already thirsty for beer and Bloody Marys.