Michael Sheen, most recently seen as David Frost in Ron Howard’s Oscar nominated “Frost/Nixon,” has signed on to play the head of the Volturi coven of vampires in “The Twilight Saga: New Moon.” Sheen must be relieved to finally shed the werewolf mask (he played a lycan in all three “Underworld” films) for that of a vampire. Boy, I know I would be. Them werewolves are stink-a-rific. Oh, and in case you’ve been in Outer Space for the last year, …