Makes it so that |cancel %force skips the next thing in the queue if
you're not in the middle of something. If you are in the middle of
something, it skips the thing you're in the middle of (just like naked
|cancel).
This should resolve issues where |cancel doesn't drain the queue.
When a ship breaches, we remove all messages that have yet to be
delivered to an app (eg if it's not yet started). We also add
|gall-sear to do this manually, but this shouldn't be needed in normal
operation.
Finally, to unblock ~zod and ~bus on mainnet, we sear one particular
ship automatically on loading hood. It cannot be done manually because
no userpace changes can be made until it's unblocked.
