Make sure to wait long enough
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
improved connz with subscriptions stats and list of subscriptions by client
added subsz and connz extended, and merged with varz
connz: limit and offset