$conf['fast_404_exts'] misses \ before .

The pattern is currently responding to anything that ends with the set extensions. Also for example update.php?id=89&op=no_js

Placing a \ infront of the . fixes this:
$conf['fast_404_exts'] = '/\.(txt|png|gif|jpe?g|css|js|ico|swf|flv|cgi|bat|pl|dll|exe|asp)$/i';