reduce this in block scopes (#2526)

fixes #2455

lib/scope.js

@@ -183,11 +183,7 @@ AST_Toplevel.DEFMETHOD("figure_out_scope", function(options){
             // scope when we encounter the AST_Defun node (which is
             // instanceof AST_Scope) but we get to the symbol a bit
             // later.
-            var parent_lambda = defun.parent_scope;
-            while (parent_lambda.is_block_scope()) {
-                parent_lambda = parent_lambda.parent_scope;
-            }
-            mark_export((node.scope = parent_lambda).def_function(node), 1);
+            mark_export((node.scope = defun.parent_scope.get_defun_scope()).def_function(node), 1);
         }
         else if (node instanceof AST_SymbolClass) {
             mark_export(defun.def_variable(node), 1);