BulletSim: don't zero motion when changing vehicle type.

Some vehicle scripts change type on the fly as an easy way of setting
all the parameters (like a plane changing to a car when on the ground).

OpenSim/Region/Physics/BulletSPlugin/BSPrim.cs

@@ -511,7 +511,10 @@ public class BSPrim : BSPhysObject
 
             PhysScene.TaintedObject("setVehicleType", delegate()
             {
-                ZeroMotion(true /* inTaintTime */);
+                // Some vehicle scripts change vehicle type on the fly as an easy way to
+                //    change all the parameters. Like a plane changing to CAR when on the
+                //    ground. In this case, don't want to zero motion.
+                // ZeroMotion(true /* inTaintTime */);
                 VehicleActor.ProcessTypeChange(type);
                 ActivateIfPhysical(false);
             });