Add a mesh-mesh distance function

[bcohen]

I'm thinking of something like the following:

double computeDistance(mesh1_triangles, mesh1_indeces, mesh1_pose, mesh2_triangles, mesh2_indeces, mesh2_pose)
// negative value denotes collision

Doesn't have to be optimized enough to be used for collision checking. Won't be used in a time critical sequence at first.