How to submit a bugfix?

I’ve been playing with a 1.3-a install (10/14) and found a bug where single_month_title is broken (due to the change from $m to $monthnum & $year). I fixed the function (found on 218 of template-functions-general.php) as well as added a space between month and year (something I think should have been implemented from the start).
Now, I’m wondering how do I get this to the developers? I’ve not done this with WP yet, so was wondering if someone could lay down the skinny for me.
BTW, the newly fixed function is now:
function single_month_title($prefix = '', $display = true ) {
global $monthnum, $month, $year;
if(!empty($monthnum)) {
$my_year = $year;
$my_month = $month[$monthnum];
if ($display)
echo $prefix . $my_month . $prefix . " " . $my_year;
else
return $monthnum;
}
}