Description:
------------
After calling "throw new Exception(..)" and entering the
function registered with "set_exception_handler()" the 
debug_backtrace() output is empty.

This is very inconvinient for self written error handling functions as "trigger_error()" for example works fine for debug_backtrace.

I'm aware that the exception itself contains a stack trace
but is there really a reason to empty debug_backtrace()?


Reproduce code:
---------------
<?php

function exception_handler($e) { debug_print_backtrace(); }

function c() { throw new Exception("Problem!"); }
function b() { c(); }
function a() { b(); }

set_exception_handler('exception_handler');
a();

?>


Expected result:
----------------
Backtrace with
#1 exception_handler from c()
#2 c() from b()
#3 b() from a()
#4 a() from main



Actual result:
--------------
#0  exception_handler(Exception Object ([] => Problem!,[] => ,[] => 0,[] => /home/ch/tt.php,[] => 5,[] => Array ([0] => Array ([file] => /home/ch/tt.php,[line] => 6,[function] => c,[args] => Array ()),[1] => Array ([file] => /home/ch/tt.php,[line] => 7,[function] => b,[args] => Array ()),[2] => Array ([file] => /home/ch/tt.php,[line] => 10,[function] => a,[args] => Array ())))) called at [(null):0]