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/MapChange.java

@@ -39,7 +39,7 @@ public class MapChange extends MapObject {
 		if (oldOne == map) {
 			oldOne.removeBacklink(parentMap);
 			map = (TMXMap) newOne;
-			newOne.addBacklink(parentMap);
+			if (newOne != null) newOne.addBacklink(parentMap);
 		}
 	}