Finished EmitCargoOnSell

The broken Lint check is still a problem after all those years. This also does not work as suggested in the empty trait. During selling it destroys the cargo so you can't just queue an Unload activity. You can't even enumerate through all passengers without hitting crashes. However, unloading just the first passenger is good enough for Red Alert's single-manned pillboxes.
I think that this would be better handled as an `EjectOnSell` parameter on CargoInfo, along with `EjectOnDeath` and `EjectOnCapture`.  They could all call a common implementation that scatters as much cargo into the adjacent cells as will fit.