Fix - AngleJoint

[Bobby5808]

Hi Jono

I had a problem with the AngleJoint, it would jump violently around
when the angle was near PI, and I fixed it by changing this line:

Scalar difference = MathHelper.ClampAngle(body1.State.Position.Angular
- body2.State.Position.Angular) - angle;

to this:

Scalar difference = MathHelper.ClampAngle(body1.State.Position.Angular
- body2.State.Position.Angular - angle);

Also, should I rather post this under issues, or is it fine putting it
in discussions?

Thanks