add textbox::set_undo_queue_length

a new method for setting the undo queue length

source/gui/widgets/skeletons/text_editor.cpp

@@ -2348,6 +2348,11 @@ namespace nana{	namespace widgets
 			_m_scrollbar();
 		}
 
+		void text_editor::set_undo_queue_length(std::size_t len)
+		{
+			undo_.max_steps(len);
+		}
+
 		void text_editor::move_ns(bool to_north)
 		{
 			const bool redraw_required = _m_cancel_select(0);

source/gui/widgets/textbox.cpp

@@ -606,6 +606,14 @@ namespace drawerbase {
 				editor->select_behavior(move_to_end);
 		}
 
+		void textbox::set_undo_queue_length(std::size_t len)
+		{
+			internal_scope_guard lock;
+			auto editor = get_drawer_trigger().editor();
+			if (editor)
+				editor->set_undo_queue_length(len);
+		}
+
 		//Override _m_caption for caption()
 		auto textbox::_m_caption() const throw() -> native_string_type
 		{