Mort Sahl did a 6-minute set last night on Mr. Letterman's show. Health-wise, he seemed older and slower. At the outset, I had the fear it would be another of those Bob Dylan moments when a one-time great embarrasses himself by trying to do what he can no longer do. But Sahl's material was sharp, and it went well. He closed with a great bit about how Jack Welch (of General Electric) and Rupert Murdoch (of News Corp) decided to direct their efforts to solving the "gang" problem in Los Angeles. One corporation went in and purchased the Crips. The other corporation acquired the Bloods. And then they both sent their accountants in to begin laying everyone off…