For a few years now, the only times to see 1946’s It’s a Wonderful Life on TV were on NBC, when the network televised it once early in December, and again on Christmas Eve. That happens again this year, which is why the classic Frank Capra Christmas movie, starring James Stewart and Donna Reed, is showing again tonight. But it doesn’t explain why, tomorrow on Christmas Day, sister corporate network E! is being allowed to present an all-day marathon of It’s