Ronald Moore and Joss Whedon seem to be trading actors lately. First Tahmoh Penikett, who played Helo on "Battlestar Galactica," joined the cast of "Dollhouse" last year. Now James Marsters, best known as Spike on Whedon's "Buffy the Vampire Slayer" and "Angel," is joining Moore's BSG prequel series, "Caprica." That's not all though. Patton Oswalt is joining the