[ODE] AMotor small changes

[George Birbilis]

> > I have done some changes in joint.cpp so that:
> > * AMotor can now be used to attach a body to the static environment.
> > * Angles passed to dJointSetAMotorParam (dParamLoStop,dParamHiStop)
> > can now be outside the (-PI,PI) range.
>
> i've checked in a modified version of these changes. the -pi..pi angle
> change is not API backwards compatible, so i left it out. also, i added
> code to handle the possibility of a reversed joint, i.e. dAttach
> (0,body). please verify that this works for you.

what do you mean by saying "not API backwards compatible"?

it's "Set" not "Get" that allows the outside -PI..PI in this addition from
what I understand (maybe internally wraps to -pi..pi the value, not sure if
that costs too much [at least one comparison at every "set" action])

however I don't see where's the problem with backwards compatibility if
"Get" will always return -pi..pi as before (or won't it?)