Since input_code() sets the nameplate before setting the rest of the code,
and since the sender's PAKE will arrive as soon as the nameplate is set, we
could got_pake before got_code, and Key wasn't prepared to handle that.
* finally wire up "application versions"
* remove when_verifier (which used to fire after key establishment, but
before the VERSION message was received or verified)
* fire when_verified and when_version at the same time (after VERSION is
verified), but with different args
