fix some out-of-date comments in btMultiBody, thanks to Thomas Buschmann

disable disactivation for btRigidBody in import urdf demo, increase strength of joint motor for btMultiBody

examples/Importers/ImportURDFDemo/MyMultiBodyCreator.cpp

@@ -32,6 +32,8 @@ class btRigidBody* MyMultiBodyCreator::allocateRigidBody(int urdfLinkIndex, btSc
     btRigidBody::btRigidBodyConstructionInfo rbci(mass, 0, colShape, localInertiaDiagonal);
     rbci.m_startWorldTransform = initialWorldTrans;
     btRigidBody* body = new btRigidBody(rbci);
+	body->forceActivationState(DISABLE_DEACTIVATION);
+	
     return body;
 }