Description:
------------
The note says, that the function 'extension_loaded' compares case-

Reproduce code:
---------------
<?php
$e = get_loaded_extensions();
foreach ($e as $k => $v) {
        $l = strtolower($v);
        $u = strtoupper($v);
        $str = "\t* check %s %s: in array %d, extension_loaded %d\n";
        printf("ext: %s\n", $v);
        printf($str, 'original', $v,
                (int) in_array($v, $e), (int) extension_loaded($v)
        );
        printf($str, 'lower-case', $l,
                (int) in_array($l, $e), (int) extension_loaded($l)
        );
        printf($str, 'upper-case', $u,
                (int) in_array($u, $e), (int) extension_loaded($u)
        );
}
exit(0);

Expected result:
----------------
ext: xmlwriter
        * check original xmlwriter: in array 1, extension_loaded 1
        * check lower-case xmlwriter: in array 1, extension_loaded 1
        * check upper-case XMLWRITER: in array 0, extension_loaded 0
ext: PDO
        * check original PDO: in array 1, extension_loaded 1
        * check lower-case pdo: in array 0, extension_loaded 0
        * check upper-case PDO: in array 1, extension_loaded 1
ext: SimpleXML
        * check original SimpleXML: in array 1, extension_loaded 1
        * check lower-case simplexml: in array 0, extension_loaded 0
        * check upper-case SIMPLEXML: in array 0, extension_loaded 0

Actual result:
--------------
ext: xmlwriter
        * check original xmlwriter: in array 1, extension_loaded 1
        * check lower-case xmlwriter: in array 1, extension_loaded 1
        * check upper-case XMLWRITER: in array 0, extension_loaded 1
ext: PDO
        * check original PDO: in array 1, extension_loaded 1
        * check lower-case pdo: in array 0, extension_loaded 1
        * check upper-case PDO: in array 1, extension_loaded 1
ext: SimpleXML
        * check original SimpleXML: in array 1, extension_loaded 1
        * check lower-case simplexml: in array 0, extension_loaded 1
        * check upper-case SIMPLEXML: in array 0, extension_loaded 1