By Robert Philpot It's pretty clear from the outset that Showtime's cancer comedy-drama The Big C doesn't intend to be a reach-for-the-tissue series about a dying woman.The series begins with Cathy (Laura Linney), a schoolteacher who has Stage IV melanoma, negotiating with a pool guy to put a pool in her back yard because, well, she wants one, even if the yard is too small (she settles for a hot tub).