[ODE] New patches: 2 new joints and some optmization

[David Walters]

> Remi Ricard wrote:
> > The first joint is a Piston. It is a joint similar to the slider but the
> > 2 bodies are free to rotate around the sliding axis.

I've added this to SVN #1305, the other joint PU is very new (8th Nov)
so I'll not add that one until it's had some time for review.

Cheers,
David

ps. Sorry Jason, I've added some more files and the rather cool piston
demo to the project -- thanks for taking the time to update them
before.