[ODE] AMotor small changes

[Benoit Chaperot]

Hi all,

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 tried those changes and in dEulerMode it worked fine for me.
The file can be downloaded at the following address:

http://www.jstarlab.com/joint.cpp

Regards
Benoit