the Redis backend supports UNIX, TCP and custom ports
no real transactions nor iteration, but it’s not needed at the moment
transactions keep replies in a freelist, which is purged on transaction
commit / abort

memcached is a distributed caching system, it is a good fit
for building resolvers with shared and replicated cache

On FreeBSD the lua package was not detected. (Tested on 9.3 and 10.1).

the build system now doesn't always relink targets

This reverts commit 17fd0612.

This reverts commit 17fd0612.