Made a mistake with the cleanupon end code. This fixes that, and does some other maintenance.

* removed a stupid save an loading bug.
* fixed typo
* Set default value for some npc.plt.
* removed one npc.die statement from mission fail. (would cause crash).
* fixed cleanup_at_end. Added null checks to mission functions. and find mission now complains when it cannot find a mission.
* removed reset npcs code. That wasn't used nor working.