this is a small step for me, but a huge step for resolver

based on _BSD_SOURCE timersub macro

this fixes stats for canceled/blocked or forwarded queries without
started name resolution

this is a first step of leaning towards LuaJIT.
the FFI bindings are much faster, simpler and don’t abort traces

daemon core scripting engine is still going to support interpreted Lua, but modules requiring library bindings (such as ‘block’) will require LuaJIT for FFI

this provides a useful callback for per-request operations that can’t wait until the query is completed (e.g. blocking or logging started queries)

The trust anchor and keys are not changed in order not to disrupt packet
validation.

this is a saner default for large answers. instead of waiting for
probably lost/thrown away fragmented packet, do the query over TCP
instead

All RRSets in section must be signed properly. (Currently no checking for
non-authoritative RRSets is implemented.)

this fixes a problem when a module was removed, but pending
queries referenced it, causing a crash. usually when the
server was busy and a module was unloaded.
as we don’t need to copy layers at all, they’re just iterated
from the array of modules using a macro