Don't mangle exported symbols

lib/ast.js

@@ -745,6 +745,16 @@ var AST_Export = DEFNODE("Export", "exported_definition exported_value is_defaul
         exported_value: "[AST_Node?] An exported value",
         is_default: "[Boolean] Whether this is the default exported value of this module"
     },
+    _walk: function (visitor) {
+        visitor._visit(this, function () {
+            if (this.exported_definition) {
+                this.exported_definition._walk(visitor);
+            }
+            if (this.exported_value) {
+                this.exported_value._walk(visitor);
+            }
+        });
+    }
 }, AST_Statement);
 
 var AST_VarDef = DEFNODE("VarDef", "name value", {