fixed type-issue for linked list indices

thanks, Nate, for reporting this issue

history.txt

@@ -1940,3 +1940,7 @@ ______
 * Objects: Prevent watcher cells from growing wider as their contents becomes taller
 * Objects: Keep watchers onstage when hiding/showing them, fixes #195
 * BYOB, GUI, locale: New preference setting for plain block prototype labels
+
+131008
+------
+* Lists: fixed type-issue for linked list indices (thanks, Nate, for reporting it!)

lists.js

@@ -61,7 +61,7 @@ PushButtonMorph, SyntaxElementMorph, Color, Point, WatcherMorph,
 StringMorph, SpriteMorph, ScrollFrameMorph, CellMorph, ArrowMorph,
 MenuMorph, snapEquals, Morph, isNil, localize, MorphicPreferences*/
 
-modules.lists = '2013-June-20';
+modules.lists = '2013-October-08';
 
 var List;
 var ListWatcherMorph;
@@ -200,11 +200,11 @@ List.prototype.length = function () {
 };
 
 List.prototype.at = function (index) {
-    var value;
+    var value, idx = +index;
     if (this.isLinked) {
-        return index === 1 ? this.first : this.rest.at(index - 1);
+        return idx === 1 ? this.first : this.rest.at(idx - 1);
     }
-    value = this.contents[index - 1];
+    value = this.contents[idx - 1];
     return isNil(value) ? '' : value;
 };