Bug 865253 - Part 2: Implement the alternate enum values for OscillatorNode; r=roc
Bug 865253 - Generate a sine wave.

This is simply a sketch which calculates a sine.

We probably want to use the PeriodicWave machinery to generate
the pre-defined waveforms anyway. Even if we do it this way
we'll evetually want caching.

Doesn't reset phase when the node is start/stopped.
I also hear some glitching.