Implement ToPolyline for Cone, Capsule and Cylinder.

Also fix the ToPolyline implementation for Cuboid.
Implement `RayCast` for the `BoundingSphere`.
Rename `BVT::new_kdtree` to `BVT::new_balanced`.

This did **not** build a kdtree.
Update to tha last rust-nightly.

Version of rustc: 0.12.0-pre-nightly (a1f497309 2014-09-09 23:55:43 +0000).