FIX: NaN point velocities would prevent system from stopping calculations when energy was below threshold

Conflicts:
	lib/arbor.js
FIX: really forced fixed points to stay fixed, rebuilt

Conflicts:
	src/physics/physics.js
Possible fix for infinite bissect in Barnes-Hut simulation
Changed __defineGetter__ and __defineSetter__ to Object.defineProperty for IE 9+ compatibility

Conflicts:

	lib/arbor.js