Previously, w.when_verified() was documented to fire only after a valid
encrypted message was received, but in fact it fired as soon as the shared
key was derived (before any encrypted messages are seen, so no actual
"verification" could occur yet).
This fixes that, and also adds a new w.when_key() API call which fires at the
earlier point. Having something which fires early is useful for the CLI
commands that want to print a pacifier message when the peer is responding
slowly. In particular it helps detect the case where 'wormhole send' has quit
early (after depositing the PAKE message on the server, but before the
receiver has started). In this case, the receiver will compute the shared
key, but then wait forever hoping for a VERSION that will never come. By
starting a timer when w.when_key() fires, and cancelling it when
w.when_verified() fires, we have a good place to tell the user that something
is taking longer than it should have.
This shifts responsibility for notifying Boss.got_verifier, out of Key and
into Receive, since Receive is what notices the first valid encrypted
message. It also shifts the Boss's ordering expectations: it now receives
B.happy() before B.got_verifier(), and consequently got_verifier ought to
arrive in the S2_happy state rather than S1_lonely.
* 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
Starting on defining manager state machines for nameplates, mailboxes, the
PAKE key-establishment process, and the bit that knows it can drop the
connection when both nameplates and mailboxes have been released.
With this, both clients and servers will send a PING at least once every
minute, and will drop connections that haven't seen any traffic for 10
minutes.
This should help keep NAT table entries alive, and will drop connections
that are no longer viable because their NAT entries have expired.
closes#60
