If you’re in New England this summer and looking for something more than a barbecue on Independence Day, why not take a cruise through Boston harbor on the world’s oldest commissioned warship afloat? A lottery for 150 open spots on the USS Constitution’s annual July 4 voyage went live Feb. 3, for the ship’s last turnaround cruise before it goes into a dry dock for repairs through 2018. Guests aboard “Old Ironsides” will enjoy a three-hour trip around the harbor, complete with 21-gun salute exchange with Fort Independence on Castle Island in South Boston. To enter, simply fill out a…