Less than two months after he left CBS' The Late Show, Letterman appeared onstage in San Antonio, Texas, Friday with Steve Martin and Martin Short, who are touring with their stage show, A Very Stupid Conversation…With Music. "Back in Hollywood, we met at a Scientology mixer," Letterman, 68, told the crowd, "and they have been so kind and so generous to invite me here to this beautiful city." "I am so happy to be out of the house," a bearded Letterman admitted. "I retired and I had no regrets—none. I was happy. I was complacent. I was satisfied. I was...