Similar functionality was implemented in upstream release 2.86 as part
of bigger optimization. While it should have introduce better
performance on bigger domain filter list, it caused several regressions
including crashes.
This is attempt to make similar functionality in different way, without
so heavy change to basic system. It instead adds new structure for each
unique domain, which tracks last tried server for a given domain. It
makes the same algorithm used for domain-less servers, such as those
read from /etc/resolv.conf. But uses that also for servers forwarding
only for subdomains.
It might slightly increase used memory on high number of local=/example/
or server=/example/::1.
Resolves: rhbz#2047510
