David Letterman said his friend Al Franken said he’d like the last show “to be mawkish or maudlin,” possibly leaning toward the former. (We think it’ll probably have a little of both.) Letterman asked bandleader Paul Shaffer for his insight, which was “I have no idea what it should be.” Letterman replied, “If we knew what to do with the last show, do you think the previous 6,000 would look the way they looked?” And then segued into a montage of some of Shaffer’s finest…