Fix for issue #874

With special acknowledgement to sxsing (his github login) for his
help in development and testing of this fix.

NOTE: Pull-request is against master as the fixes branch has not
been updated with the v1.5 file src/handle_connect.c

Signed-off-by: Dave Miller <dmiller@tibco.com>

src/handle_connect.c

@@ -578,6 +578,7 @@ int handle__connect(struct mosquitto_db *db, struct mosquitto *context)
 		}
 
 		found_context->clean_session = true;
+		found_context->state = mosq_cs_expiring;
 		do_disconnect(db, found_context);
 	}
 

src/loop.c

@@ -608,7 +608,9 @@ void do_disconnect(struct mosquitto_db *db, struct mosquitto *context)
 			}else{
 				id = "<unknown>";
 			}
-			if(context->state != mosq_cs_disconnecting){
+			if (context->state == mosq_cs_expiring){
+				log__printf(NULL, MOSQ_LOG_NOTICE, "Expiring old client session %s, disconnecting.", id);
+			}else if(context->state != mosq_cs_disconnecting){
 				log__printf(NULL, MOSQ_LOG_NOTICE, "Socket error on client %s, disconnecting.", id);
 			}else{
 				log__printf(NULL, MOSQ_LOG_NOTICE, "Client %s disconnected.", id);