[ODE] 2D

[David Walters]

> I didn't make any changes the joint beyond what needed to be done to make it
> work.

That's good to hear - it means you've got a great test case for
verifiying the 2D joint. Were there any additional support functions
required?

I think you have to reset the rotation and a.velocity every time step
to correct drift - It seems like if a generic function for doing that
or even an automatic feature for bodies was part of ODE then a lot
less user code would be needed for things like upright capsules -- my
engine has a post ODE step, I reckon most people have one... what do
people think about formalising that process?