[ODE] test_boxstack fails

[Roger Luethi]

If DEBUG_LCP in lcp.cpp is enabled, test_boxstack dies on the first
box or cylinder. Spheres take somewhat longer to get there:

ODE INTERNAL ERROR 1: assertion "p[k] >= 0 && p[k] < i" failed in
checkPermutations() [ode/src/lcp.cpp]

Is the assertion checking just overzealous, or is this a bug?

I am particularly interested in this because I noticed that some
simulation of mine goes unstable just a few world steps after this
assertion fails.

Roger