[ODE] Actuated arm get stuck into static entities

[Denes Nagymathe]

As far as i know, this is normal. ODE keeps the joints (and geoms, and 
bodies, etc.) in linked lists, and the quickest way to add a new node is to 
insert it to the head. So don't expect any of those 'indices' to remain 
fixed. Better keep the pointers (or dJointID, dBodyID, dGeomID, etc.) for 
yourself; just watch out for deletions.
(As you can check it for yourself too, dBodyGetJoint() just traverses 
through the joint list of the given body, counting 'til reaches the given 
index. Not the fastest way to access a node, but works.)

Denes