In the old days, you would check in on an alien-visitation shlock-TV documentary (or an episode of “Unsolved Mysteries”) all to catch those grainy home-movie glimpses of alien spaceships. On that score, “Close Encounters of the Fifth Kind” is nothing less than an all-you-can-eat banquet of UFO porn. There are vintage clips of “sightings” shot in 8 and 16mm,