New TickedVehicle.Stop method

Previously, when update realized that the vehicle could not move it would
zero its velocity, to avoid having left-over velocity move the vehicle
when it was re-enabled and before the new direction was re-calculated.

I've decided to separate this into an explicit Stop() method, since I
don't really like the idea of having a hidden velocity alteration. Users
may want to move the vehicle somewhere else on their own, while having it
continue at its previous speed when re-enabled.

Behaviors/TickedVehicle.cs

@@ -292,21 +292,11 @@ protected void AdjustOrientation(float deltaTime)
 
 	void Update()
 	{
-		// We still update the forces if the vehicle cannot move, as the
-		// calculations on those steering behaviors might be relevant for
-		// other methods, but we don't apply it.  
-		//
-		// If you don't want to have the forces calculated at all, simply
-		// disable the vehicle.
 		if (CanMove)
 		{
 			ApplySteeringForce(Time.deltaTime);
 			AdjustOrientation(Time.deltaTime);
 		}
-		else 
-		{
-			ZeroVelocity();
-		}
 	}
 
 	[System.Diagnostics.Conditional("TRACE_ADJUSTMENTS")]
@@ -318,6 +308,12 @@ void TraceDisplacement(Vector3 delta, Color color)
 		}
 	}
 
+	public void Stop()
+	{
+		CanMove = false;
+		ZeroVelocity();
+	}
+
 
 }