[ODE] Possible solution to unstable rotating bodies problem

[Tyler Streeter]

This refers to the problem where energy is added to rotating bodies
(especially long, thin objects) due to numerical inaccuracy from
explicit integration, described here:

http://ode.org/ode-latest-userguide.html#sec_12_12_0

Here's my idea to alleviate this problem:

1. Store each body's previous angular velocity (just the magnitude
should be enough).
2. Every time step, check the bodies to see if they are "freely
spinning," which is true if no contacts have been made with the body
and no user forces have been added in the last time step.
3. If a body is freely spinning and its current angular velocity is
greater than the previous angular velocity (i.e. by comparing
magnitudes), then make the current angular velocity magnitude equal to
that of the previous step (normalize the current angular velocity and
scale it by the previous magnitude).

This should ensure that freely spinning bodies can never increase
their angular velocity.  Does this seem like a good solution?  Any
other ideas?

Tyler