When “Political Animals” finishes shooting, see if you can follow Weaver’s schedule: she goes right into a new Christopher Durang play for a short run at Lincoln Center. Then she films “Avatar” 2, 3, and 4 with James Cameron. That’s right: they’re making three sequels to the blue 3D phenom all at the same time. Weaver says she has no idea how long it will take, or how it’s going to work. “I just show up,” she said.