Description:
------------
ctype_alpha fails to identify at least two iso-8859-15 characters: s-caron (?) and z-caron (?) and their upper-case equivalents.

Reproduce code:
---------------
<?php
setlocale(LC_ALL,'et_EE');
header("Content-Type: text/html; charset=iso-8859-15;");
$strings = array('???aa','sete','a?ew', 'a?e','????','te?t','?ombie');
foreach ($strings as $testcase) {
	if (ctype_alpha($testcase)) {
		echo "Alpha test - $testcase - PASSED.<br />\n";
	} else {
		echo "Alpha test - $testcase - FAILED.<br />\n";
	}
}
?>

Expected result:
----------------
Alpha test - ???aa - PASSED.
Alpha test - sete - PASSED.
Alpha test - a?ew - PASSED.
Alpha test - a?e - PASSED.
Alpha test - ???? - PASSED.
Alpha test - te?t - PASSED.
Alpha test - ?ombie - PASSED.

Actual result:
--------------
Alpha test - ???aa - PASSED.
Alpha test - sete - PASSED.
Alpha test - a?ew - FAILED.
Alpha test - a?e - FAILED.
Alpha test - ???? - PASSED.
Alpha test - te?t - FAILED.
Alpha test - ?ombie - FAILED.