[ODE] saving internal joint state

[Matthew D. Hancher]

This is related to a question I asked earlier, but viewed from a
different angle.

Suppose you want to take a snapshot of a running ODE simulation, so
that you can go back and have it replay *exactly* from that point.
This requires saving some internal joint state, but there does not
appear to be any straightforward way to reload that state (or even get
at all of it).  For instance the anchor points of a ball joint may be
slightly separated, but dJointSetBallAnchor() always makes the two
anchor points coincident.

Am I missing something here?  Comments on the Wiki suggest that 
some people do perfect saves/reloads; how did you approach this?

mdh

Matt Hancher
NASA Ames Research Center
Official: mdh at email.arc.nasa.gov
Personal: mdh at media.mit.edu