Actors get to try a little bit of everything but this seems to be the month of submerging those scamps. James Cameron, however, does not own the market on professional-grade dunk tanks (even if he's tried really, really hard). Much like how nearly every videogame features the requisite water level, a significant chunk of Hollywood finds itself clocking in a few hours beneath the waves. "Harry Potter" did it at least twice, "Mission Possible" did it in "Rogue Nation," and even "The Shape of...