Sphere/box collisions for voxels, various utility functions.
Capsule/box collisions.
Fix for NaN.
Merge branch 'master' of https://github.com/worklist/hifi
Fixed Linux build error and a warning on call to Avatar.simulate, moved grid
size constant to world.h and made gravity bounds match.
Merge pull request #437 from ey6es/master

Sphere/box and capsule/box collisions for voxels; allows us to slide along and stand on voxels.  Also a couple build fixes.