Description:
------------
restore_error_handler() returns always true, no info.
But in complex situations where included files could add other handlers, there's no way to be sure that the restored handler is the wanted one.

This doubt could be prevented if restore_error_handler() would return the actual callable or null if at the end of the stack.


Test script:
---------------
file1.php
=========
<?php
set_error_handler('someFunct');
include 'file2.php';
restore_error_handler(); // Not enough!

file2.php
=========
<?php
set_error_handler('anotherFunct');

Expected result:
----------------
NOT CORRECT! It could be an useful feature

file1.php
=========
<?php
$prev = set_error_handler('someFunct');
include 'file2.php';
do {
   $actual = restore_error_handler(); // Run twice
} while ($actual != $prev);

file2.php
=========
<?php
set_error_handler('anotherFunct');