[ODE] Plane-Cylinder collision: not good in 0.7, worse in SVN :(

[David Walters]

Just to add that test_heightfield (SVN #1099) triggers the assert when
you drop a cylinder onto it.

The depth assert is triggering dIASSERT(Contact->depth >= 0.0) with a
contact depth of around -3.7591648 on the first occurrence.

Replacing with the lines (in both places):

	if ( Contact->depth >= 0 )
	{
		dIASSERT(Contact->depth >= 0.0);
		nContacts++;
	}

works approximately, however the cylinder doesn't sit very stably on
the heightfield surface.

Hope this helps

Regards,
David