IPv6Route: add a pointer to the routing table
RoutingTable6: cache update fix from ANSARoutingTable6
IPv6Route: added 'adminDist' and 'routingProtocolSource' fields, and change notifications
RoutingTable6: sort routes by administrative distance, then by metric

so the metrics are compared only if the routes have the same adm. distance.
AnsaRoutingTable6: remove unneeded methods

prepareForAddRoute() is not needed, because the route is always added
to the routing table. It is not used, if there is a better one.
RoutingTable6: setting administrative distances
RoutingTable6: create new routes with a factory method

so subclasses can use their own route types
RoutingTable6: remove entries from the destination cache when the interface gets deleted or is down
cosmetic changes