UAC dirty script for better windows integration to create symlinks. More

data using a thread-safe collection. Some NPEs fixed. 
More data protection in tiled integration functions (better state
checking, backup tiled-made file before saving ATCS-made data).
jardesc file added for convenience.

src/com/gpl/rpg/atcontentstudio/model/maps/SpawnArea.java

@@ -66,7 +66,7 @@ public class SpawnArea extends MapObject {
 		if (replacedIndex >= 0) {
 			oldOne.removeBacklink(parentMap);
 			spawnGroup.set(replacedIndex, (NPC) newOne);
-			newOne.addBacklink(parentMap);
+			if (newOne != null) newOne.addBacklink(parentMap);
 		}
 	}