Description:
------------
isConstructor() should return true for child classes as well, but it does not.

Reproduce code:
---------------
<?php
class t
{
    function __construct(){}
}
class e extends t {}
$a = new ReflectionMethod('t','__construct');
$b = new ReflectionMethod('e','__construct');
var_dump($a->isConstructor());
var_dump($b->isConstructor());

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

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