Once a major shipbuilding and commercial fishing center that fell on hard times, Belfast, Maine, is enjoying a revival that makes it an attractive cruising destination this summer if you’re heading Down East. Way up Penobscot Bay, Belfast seems a bit off the beaten track, but it’s well worth the detour. For one thing, the newly invigorated waterfront, centering around a public Harbor Walk and the thriving Front Street Shipyard, is worth a visit in itself. For another, because of its location, Belfast often gets less summer fog than many other Maine ports. Belfast dates to 1630, when it was…