NSD 4.1.18 released

This release has features for saving memory and faster notification.With --enable-packed, 33% memory savings could be had, or somethingalong that size. Notification of secondary servers happens in parallel,and has faster timeouts. More sockets are used for zone transfers.This speeds up communication with a larger set of servers. Additionallya bug is fixed for dual-loaded parent-and-child zone configured at thesame time, when one of the zones has not loaded properly.