The handler which is invoked for every node for which is trace is found. The user should
implement this handler with an appropriate action, e.g. selecting all this nodes in a layer,
storing them into a list, building up a new graph, ...
aNode - the node for which is trace is found.
aShortestRoute - the route leading from the preceding/succeeding route to this node. The
preceding/succeeding route will not be a part of this route.
aDistance - the distance of this shortest route, calculated in terms of the
ILcdEdgeValueFunction that was given as an argument to the