xversion: the rig cannot pass client flags per leg, so -A against an old daemon stays a hand check

open   by a73x

An `-A` client against a pre-agent-forwarding daemon should degrade quietly:
the daemon never sends `agent_open`, so nothing is forwarded and nothing
breaks. Verified by hand when agent forwarding landed; not codified, because
every xversion leg drives its client with a fixed argv and there is nowhere
to add `-A` for one leg only.

Same change the epoch-pin issue wants — see 45f73db2. Filing separately so
the agent-forwarding side of it is findable from this feature's own trail.