Merge pull request #39 from pdewacht/master

Partially fix Arbror
Fix a missing parameter with the surprise wall dialog.
Fix a typo in French dialogs.
Fix all errors with destination being possibly nil.
Fix dungeon 3 miniboss.
Fix entity names in dungeon 3 to call set_entities_enabled() correctly.
Billy's cave: function billy_leave() referenced before definition
Fix bandit fight in smith's cave
attempt to index global 'lamp' (a nil value)

At this point in the game the lamp is no longer available. So `lamp:remove()`
fails because `lamp` is nil.