Added session timeouts.

The parameter 'connection_timeout' for services takes a value as seconds.
All sessions that have been idle for longer than this will be disconnected.

server/modules/protocol/mysql_client.c

@@ -576,6 +576,8 @@ int gw_read_client_event(
         CHK_PROTOCOL(protocol);
         rc = dcb_read(dcb, &read_buffer);
         
+	dcb->last_read = hkheartbeat;
+	
         if (rc < 0)
         {
                 dcb_close(dcb);