When you first boot, if you try talk to someone before your azimuth is
up-to-date (for example by import), then if they've ever breached
(twice) then you'll get breach notification, cancelling your message.
This changes is it so that if we haven't heard anything about this ship,
we don't signal a breach.
The implementation complexity is primarily because we need
eth-watcher/azimuth-tracker to produce an update of a list instead of a
list of updates. This way, Jael can keep a "state as of the beginning
of this move" variable to check when deciding whether to signal a
breach.
To 30 blocks + 30 blocks + 0-5 minutes == about 15 minutes total.
Further reduction should be possible, but requires changing the
algorithm a bit. We don't want to reduce the number of confirmations
below about 30, though, since we don't handle reorganizations well.
See #2414.
