ensure unique names when renaming costumes

gui.js

@@ -5533,12 +5533,13 @@ CostumeIconMorph.prototype.editRotationPointOnly = function () {
 
 CostumeIconMorph.prototype.renameCostume = function () {
     var costume = this.object,
+        wardrobe = this.parentThatIsA(WardrobeMorph),
         ide = this.parentThatIsA(IDE_Morph);
     new DialogBoxMorph(
         null,
         function (answer) {
             if (answer && (answer !== costume.name)) {
-                costume.name = answer;
+                costume.name = wardrobe.sprite.newCostumeName(answer);
                 costume.version = Date.now();
                 ide.hasChangedMedia = true;
             }

history.txt

@@ -2208,4 +2208,4 @@ ______
 140718
 ------
 * Lists: incorporate Brian’s adhoc fixes, thanks, Brian!
-* GUI: Use new mechanism for unique costume names on the paint editor
+* GUI: Use new mechanism for unique costume names on the paint editor, renamed costumes