Without this, the Follower would see data for subchannel 0 before it had a
chance to create the SubChannel object that could accept it. We already have
a mechanism for inbound data to be queued inside the SubChannel until the
endpoint has had a chance to create the Protocol object: we rely on that
mechanism here. We just need to create the SubChannel before telling the
Manager to start, even though we don't reveal the SubChannel to the
caller (via the control endpoint) until the connection is known to succeed.
This helps a manual test get data from one side to the other without throwing
exceptions.
Dilator.stop() now shuts everything down, and returns a Deferred when it all
stops moving. This needed some Manager state machine changes (to notify
Dilator when it enters the STOPPED state). This also revealed problems in the
delivery of connector_connection_made() (which was misnamed) and
connector_connection_lost() (which wasn't being called at all).
This is only used by tests so far (and will simplify the integration test
that hasn't landed yet), but is not yet wired up to Boss, so there's no way
for applications to enable it yet.
