Critical emergency patch.

This patches a game breaking bug in Sandcastle. If you have a save already, you'll need to skip that level using the cheat idlev 20. If you start a new game after this patch, you should be fine. I'm really sorry about this everybody. Let me know if you find any bugs.

Thanks to Lancer-X for finding all these bugs. I would never have known about these without him.

I also reverted most of the difficulty changes in one way or another. Some parts are probably easier than before, others harder, probably a wash overall. Difficulty is hard to get right :( Let me know if anything is too easy or too hard, if there's anywhere with too little ammo or too much.