Add Close menu item to the notebook tab menu

This is especially useful if tab close buttons are disabled.

src/notebook.c

@@ -246,6 +246,12 @@ static void show_tab_bar_popup_menu(GdkEventButton *event, GtkWidget *page)
 	gtk_widget_show(menu_item);
 	gtk_container_add(GTK_CONTAINER(menu), menu_item);
 
+	menu_item = gtk_image_menu_item_new_from_stock(GTK_STOCK_CLOSE, NULL);
+	gtk_widget_show(menu_item);
+	gtk_container_add(GTK_CONTAINER(menu), menu_item);
+	g_signal_connect(menu_item, "activate", G_CALLBACK(notebook_tab_close_clicked_cb), page);
+	gtk_widget_set_sensitive(GTK_WIDGET(menu_item), (page != NULL));
+
 	menu_item = ui_image_menu_item_new(GTK_STOCK_CLOSE, _("Close Ot_her Documents"));
 	gtk_widget_show(menu_item);
 	gtk_container_add(GTK_CONTAINER(menu), menu_item);