Description:
------------
ctype_lower detects non-lower characters when the local is set to 'en_US.UTF-8' 
on Mac OSX 10.8. This phenomenon cannot't be reproduced on Ubuntu Linux.

This phenomenon means ctype_lower detects Chinese characters and Hangul (Korean 
Alphabet) which have no concept about lower and upper cases.

The test cases for C language and showing misdetected characters can be seen 
here: 
https://gist.github.com/masakielastic/5828106

The tests for BSD-compatible OSes are needed judging from Xcode's manual. 

http://developer.apple.com/library/Mac/documentation/Darwin/Reference/ManPages/m
an3/islower.3.html

ctype_upper also detects non-upper characters.

Test script:
---------------
$expected = [];
$result = [];
 
for ($i = 0; $i <= 0xFF; ++$i) {
 
    setlocale(LC_ALL, 'C');
    if (ctype_lower(chr($i))) {
        $expected[] = $i;
    }
 
    setlocale(LC_ALL, 'en_US.UTF-8');
    if (ctype_lower(chr($i))) {
        $result[] = $i;
    }
 
}
 
var_dump(
    [] === array_diff($result, $expected)
);

Expected result:
----------------
bool(true)

Actual result:
--------------
bool(false)