Treat interposes in a new area as cancelling the old area's berth
- This should hopefully fix some thorny problems in the West where we would get a new area interpose followed by an old area cancel when migrating area boundaries -- which would fuck up the SMART logic and result in it not recording the cancel properly.
- (...as well as having the train potentially time out if delayed, which is stupid)
- To fix this, we treat any cross-area interpose as potentially cancelling the previous berth, and then ignore the cancel if we did this.