Tracking Drop-Down does not work correctly

Two Parts:

1) user-specific options

On the tracking page (/users/tracking-index.php), the
drop-down list allowing you to select a username to
show assigned tickets to was not working. No matter
which username I would select, it would show no
currently assigned tracking items.

I changed line 75 of the tracking-index.php file from:
"$opts["u:$id"] = sprintf(_("Show only tracking
assigned to %s"), $name);"

to:

$opts["u:$name"] = sprintf(_("Show only tracking
assigned to %s"), $name);

It now uses the $name (user's username) as a value in
the select option rather than the id number. This
yields correct results on the page.

2) all and nobody options

On the same drop-down list, there are currently two
blank lines that appear. They are supposed to be
options to select all tracking items or any item not
assigned to anyone.

An array of options is created on lines 70 - 72 of
tracking-index.php.

Those lines look like this after installing 1.5.5:
$opts = array('all' => __("Show All Tracking"),
'unassigned' => __("Show only tracking not assigned
to anyone")
);

I modified them so they look like this:
$opts = array('all' => "Show All Tracking",
'unassigned' => "Show only tracking not assigned to
anyone"
);

Now those top 2 options work fine.

If someone gets a few spare moments, could they e-mail
me what the purpose of the __() function is? I'm just
a PHP dabbler and can't figure it out.