fix AST_Scope.clone() (#2803)

fixes #2799

lib/ast.js

@@ -308,6 +308,13 @@ var AST_Scope = DEFNODE("Scope", "variables functions uses_with uses_eval parent
         enclosed: "[SymbolDef*/S] a list of all symbol definitions that are accessed from this scope or any subscopes",
         cname: "[integer/S] current index for mangling variables (used internally by the mangler)",
     },
+    clone: function(deep) {
+        var node = this._clone(deep);
+        if (this.variables) node.variables = this.variables.clone();
+        if (this.functions) node.functions = this.functions.clone();
+        if (this.enclosed) node.enclosed = this.enclosed.slice();
+        return node;
+    }
 }, AST_Block);
 
 var AST_Toplevel = DEFNODE("Toplevel", "globals", {