public void setSafeMargin( ref btVector3 halfExtents, double defaultMarginMultiplier = 0.1f )
{
//see http://code.google.com/p/bullet/issues/detail?id=349
//this margin check could could be added to other collision shapes too,
//or add some assert/warning somewhere
double minDimension = halfExtents[halfExtents.minAxis()];
setSafeMargin( minDimension, defaultMarginMultiplier );
}