Fixed the Tiberian Sun harvester

Got it to a state where it does not crash. Replacing voxel animations does not work as I hoped though.
It also sets us up for trouble in the future if somebody wants to introduce multiple levels of docking: e.g. a harvester that deploys drones to harvest, and then returns back to a refinery to unload.  This needs the ability to distinguish between "something docking with me" and "i'm docking with something else".