COME RUN WITH US in late March down the streets of old Mobile, where in early spring the city is in full bloom. The pink hues of azaleas mingled with the white blossoms of dogwood and bridle wreath are everywhere in sight, and the sweet fragrance of purple wisteria drifts gently in the air. Thousands of runners race down the oak-shaded streets lined by magnificent old homes that evoke images of a time long past.