Description:
------------
when i tried to match nested patterns my apache2 with php crashed - however for similar inputs a very similar regular expression is in use and causes no problems... (but the crash seems to be related to the number of nesting levels)

Reproduce code:
---------------
<?php
	//long test string -> crash
	$match= "{IF(a)}if{IF(a)}fi{IF(a)}if{ELSE}else{/IF}{ELSE}else{IF(a)}if{ELSE}else{/IF}{/IF}{ELSE}else{IF(a)}if{ELSE}else{IF(a)}if{ELSE}else{/IF}{/IF}{/IF}";
	//shorter test string -> still crash, but if 1 remove the first nested {IF... it doesnt crash any more
	$match= "{IF(a)}if{IF(a)}fi{ELSE}else{/IF}{ELSE}else{IF(a)}if{ELSE}else{/IF}{/IF}";
	$reg= '/\{IF\((.*)\)\}([^\{]+?)(\{ELSE\})?([^\{]*?)(\{\/IF\})/Us';
	$matches= array();
	function cback($t) { global $matches; $matches[]= $t; return '';}
	preg_replace_callback($reg, 'cback', $match);
	var_dump($matches);
?>

Expected result:
----------------
array with the mathes of the regExp correctly nested... but i was in the stage of designing the regular expression itself - at least i did not expect a crash...

Actual result:
--------------
Apache/2.2.10 (php loaded as module) error_log:
without 3rd party extensions:
[notice] child pid 11335 exit signal Segmentation fault (11)
with XDebug enabled:
[error] [client 127.0.0.1] ALERT - possible memory corruption detected - unknown Hashtable destructor (attacker '127.0.0.1', file '/path/file.php')
when running php from the command line (no crash -> no backtrace):
$ php reproduce.php #same content as the code posted above!
array(2) {
  [0]=>
  *RECURSION*
  [1]=>
  *RECURSION*
}
ALERT - possible memory corruption detected - unknown Hashtable destructor (attacker 'REMOTE_ADDR not set', file 'unknown')