$('select option[value="'+oSettings._iDisplayLength+'"]', nLength).attr("selected", true);
should be
$('select option[value="'+oSettings._iDisplayLength+'"]', nLength).prop("selected", true);
When using jQuery 1.9. jQuery Migrate 1.0.0 plugin, the following message is issued when .attr("selected", true) is used:
"JQMIGRATE: jQuery.fn.attr(selected) may use property instead of attribute"
