UPBGE: Fix angular velocity motion servo with little objects.

Previously the force computed in servo control logic brick was multiplied
by the mass. This behaviour is correct because bullet in
btRigidBody::integrateVelocities compute the linear velocity using force / mass.
But the angular velocity doesn't use this formula. For the angular
velocity we have to multiply the torque by the inertia of the body because
bullet compute angular velocity with: torque * inertia_tensor.

source/gameengine/Ketsji/KX_ObjectActuator.cpp

@@ -188,8 +188,15 @@ bool KX_ObjectActuator::Update()
 
 			MT_Vector3& f = (m_bitLocalFlag.ServoControlAngular) ? m_force : m_torque;
 			f = m_pid.x() * e + m_pid.y() * I + m_pid.z() * dv;
-			// to automatically adapt the PID coefficient to mass;
-			f *= mass;
+
+			/* Make sure velocity is correct depending on how body react to force/torque.
+			 * See btRigidBody::integrateVelocities */
+			if (m_bitLocalFlag.ServoControlAngular) {
+				f = f * parent->GetLocalInertia();
+			}
+			else {
+				f *= mass;
+			}
 
 			const bool limits[3] = {m_bitLocalFlag.Torque, m_bitLocalFlag.DLoc, m_bitLocalFlag.DRot};