TeeAction: copy the DNS traffic stream

This action sends off a copy of a UDP query to another server, and keeps statistics on the responses received. Sample use:

> addAction(AllRule(), TeeAction("192.0.2.54"))
> getAction(0):printStats()
refuseds    0
nxdomains   0
noerrors    0
servfails   0
recv-errors 0
tcp-drops   0
responses   0
other-rcode 0
send-errors 0
queries 0

It is also possible to share a TeeAction() between several rules. Statistics will be combined in that case.