Description:
------------
The sorting function used in the example of uasort() is incorrect because it will 
cause elements with equal values to still be swapped. Sorting functions should 
never return a value of 0. It should always be either -1 or 1.

Test script:
---------------
This is the exact sorting example from http://php.net/manual/en/function.uasort.php:

<?php
// Comparison function
function cmp($a, $b) {
    if ($a == $b) {
        return 0;
    }
    return ($a < $b) ? -1 : 1;
}

// Array to be sorted
$array = array('a' => 4, 'b' => 8, 'c' => -1, 'd' => -1);
print_r($array);

// Sort and print the resulting array
uasort($array, 'cmp');
print_r($array);
?>

Expected result:
----------------
To not have the 'c' and 'd' elements swapped.

<?php
Array
(
    [a] => 4
    [b] => 8
    [c] => -1
    [d] => -1
)
Array
(
    [c] => -1
    [d] => -1
    [a] => 4
    [b] => 8
)
?>

Actual result:
--------------
The 'c' and 'd' elements are swapped, even though they had the same values.

<?php
Array
(
    [a] => 4
    [b] => 8
    [c] => -1
    [d] => -1
)
Array
(
    [d] => -1
    [c] => -1
    [a] => 4
    [b] => 8
)
?>