[ODE] Creating a 2d wrapper class around the ODE lib

[David Walters]

> I would like to see a good Plane2D joint in the trunk; I think this is
> being worked on.

I've had a quick look at Plane2D and in the process I've successfully
integrated it into the latest ODE. Also "test_plane2d" seems to be
working... does anyone object to me to checking this into SVN at this
time ?

With this base we can start working towards something even better...

Regards,
Dave.