Missing destroy(s) for rwlocks, mutexes and conditions

It was reported to us that there's a runaway memory leak on FreeBSD which was identified as missing dtor for pthread primitives:

1. sock->cond in netmgr - the one causing runaway memory use
2. worker->lock - one per worker
3. rwlocks in db.c and dlz.c - initialized once per named (fixing would require dtor at library unload, not worth fixing)
4. rwlock in lib/*/result.c - initialized once per named (fixing would require dtor at library unload, not worth fixing)