CPAnimation frame rate fixes.

CPAnimation always schedules timers with a repeat interval of 0.0, regardless of previous calls to setFrameRate:. A while ago CPTimer was changed to treat a time interval of 0.0 as 0.1, correctly reflecting NSTimer behaviour. This causes all CPAnimations to look choppy.

Patch content:
- Respect frameRate when scheduling timer in CPAnimation.
- Treat a frameRate of 0 as "really fast" instead of CPTimer default (10 fps).
- Test cases