Local to Local replication duplicates remote ID

Local to local replication accidentally bases its remote DB ID on the local database instead of the remote one.  This is because of a quirk of how LoopbackProvider works.  There are actually two sockets (one for the client side and one for the server side) each containing their own URL as the url property.  However, the remote DB ID logic consults the url of the socket to use as its lookup key and since it returns its own URL instead of the URL of the destination, every local to local replication on a given local database will end up with the same key and thus bad things can happen with remote ancestors.