Blender Git Loki

Improved damping calculation.

Now actually uses the damping substeps setting. Damping happens as an
additional step _after_ the main force calculations. Note that it
updates the next.velocity based on the next.velocity itself, unlike the
actual semi-implicit Euler step, which works with the previous velocity.
This makes damping much more accurate by letting it work with the
changed velocities right away before they introduce too much energy into
the system.