This should speed up the protocol, since we don't have to wait for
acks (HTTP responses) unless we really want to. It also makes it easier
to have multiple messages in flight at once. The protocol is still
compatible with the old HTTP version (which is still used by the
blocking flavor), but requires an updated Rendezvous server that speaks
websockets.
set_code() no longer touches the network: it just stores the code and
channelid for later. We hold off doing 'claim' and 'watch' until we need
messages, triggered by get_verifier() or get_data() or send_data().
We check for error before sleeping, not just after waking. This makes it
possible to detect a WrongPasswordError in get_data() even if the other
side hasn't done a corresponding send_data(), as long as the other side
finished PAKE (and thus sent a CONFIRM message). The unit test was doing
just this, and was hanging.
Also, we now disable confirmation to exercise a verifier mismatch. An
upcoming implementation change can probably detect the mismatch too
early otherwise, and throw WrongPasswordError before the test can
compare the verifiers.
This allows the Wormhole setup path to be simpler: consistently doing a
claim() just before watch(), regardless of whether we allocated the
channelid (with get_code), or dictated it (with set_code or
from_serialized).
The websocket lives on a Resource of the main rendezvous web site, and
the websocket URL is derived from the main "relay_url", so there's no
extra port to allocate, and no extra service to shut down.
