entity:set_enabled(true) does not work if it blocks the hero
Created by: christopho
When you enable an obstacle entity that overlaps the hero, it avoids to block the hero and instead waits for the hero to leave before getting enabled. This is an old feature that does not make a lot of sense. If the user wants to do so, the script should do it.
See http://forum.solarus-games.org/index.php/topic,492.msg2365.html#msg2365
Fixing this problem will break compatibility because old games (like zsdx in dungeon 2) expect this behavior.