If you've just tuned back in to Nicaragua (as the airwaves slowly drain of The Summit), those aren't re-runs you're watching, folks. Not that there isn't a certain sense of deja vu. The Sandinistas just shot down another American, this one named Denby, who was connected with the contra resupply network. Only last Christmas it was a captured flyboy named Hasenfus who was in the news, released as a "good-will gesture" by President Daniel Ortega. And there were fresh claims this week that the "humanitarian" aid to the contras, approved just months ago, is once again being used - as it was in 1985 - to slip weaponry into the jungles. Makes you wonder whether the networks are planning a sequel to the Iran-contra hearings for next summer.