Only update raycasts once per frame.

Since touch events can happen multiple times per rendered frame,
this ends up being significant, and gets us up to 55-56 fps
with visibility polygon rendering turned on. Right now, the profiler
indicates that the majority of our time spent per frame now is
in calling setVertexPosition on Quad, and in sorting the intersections
by angle. Will need to investigate those further...
Merge branch 'master' of github.com:southpawfishel/VisibilityTest