The mild winter let officials probe Round Valley Reservoir for six men missing for years. CLINTON, N.J. - Authorities call it "New Jersey's Bermuda Triangle," a watery place where people disappear. The description held true yesterday after a 41/2-hour search of the Round Valley Reservoir in Hunterdon County failed to turn up any trace of six missing boaters and fishermen, some last seen in 1973. Weather and water conditions were ideal this week for an expanded search: A relatively dry winter has left the 180-foot-deep reservoir eight feet below normal, exposing an additional 30 to 90 feet of shoreline. Thirty...