Jeff Barr spam hack modification

I’m trying to make Jeff Barr’s spam hack case INsensitive.
I added this line:
$jeff = strtolower($jeff);
above these lines in wp-comments-post.php
$jeff = trim($_POST[’jeff’]);
if ( ‘Jeff’ != $jeff )
die("You forgot Jeff’s first name. If you are forgetful, hit Back and try again. “);
but it still won’t approve the comment if the user enters “JEFF” or “jeff”… What am I doing wrong? Of course I’m using a different verification question — just keeping this example simple.