Description:
------------
If you set an error handler when inside an error handling function, set_error_handler will always return NULL.

Test script:
---------------
<pre>
<?php

function first_handler () {
		echo "  first_handler\n";
		echo '     Set to second handler: <strong>', gettype (set_error_handler ('second_handler')), "</strong>\n";
		echo "\n\n", '$y = $o', "\n";
		$y = $o;
}
function second_handler () {
		echo "  second_handler\n";
}

set_error_handler ('first_handler');
echo '$x = $y', "\n";
$x = $y;
echo '     Set to other handler: <strong>', gettype (set_error_handler (function(){})), "</strong>\n";


Expected result:
----------------
set_error_handler should return the name of the error handling function, which in this case would be the name of the running function.

Actual result:
--------------
It just returns null.