Retry: Fix subscription sharing/route reconnect race that causes some clients not to receive messages

Replaces #49 b/c I need that branch without force push

No longer add subscriptions to router clients with no existing connection.

race condition:
 - a client is closed at the same time as an incoming SUB message occurs.
 - the subscription is added to the srv.sl even though the socket is
   closed.
 - the connection cleanup has already run, so the bad state is never
   corrected
 - now messages may be forwarded to a client without a connection
 - messages will not be forwarded to a router that needs it now, because
   processMsg assumes the router already received it