* SECURITY UPDATE: unbounded cache-cleanup event queue lets a query pattern drive named past max-cache-size - debian/patches/CVE-2023-6516.patch: send tree-pruning events to a dedicated rbtdb pruning task whose quantum is effectively unlimited instead of the quantum-1 rbtdb->task, so the pruning queue drains at least as fast as it is fed; traverse every eligible ancestor in one prune_tree() execution; create the cache database tasks in cache_create_db() so a cache flush keeps pruning alive - takes upstream's final 9.16.49 design (GL #4596, GL #4621) and not the superseded prunenodes-list design, so struct dns_rbtnode is unchanged and MAPAPI stays at 1.1 - only decrement_reference() queues prune events on 9.10.3; cleanup_dead_nodes() drains synchronously and is left untouched - dns_db_settask() takes a second task argument; no reverse dependency in this ELS set consumes that symbol - CVE-2023-6516