[ODE] solving penetrations "statically"

[Andres James]

Here's a test modification to ODE using Erin's "Split PGS" idea to
resolve penetrations more gracefully, demo included:

http://andres.ediy.co.nz/files/test_split-sor.zip

It seems to work okay, but I'm not certain my changes are correct...
Also the final position update is just hacked in, it needs to be
properly integrated with dxStepBody (as it currently doesn't apply any
rotational error correction at all).