Description:
------------
While trying to craft a relatively complex regex string I caused php to consistently segfault.  I then tracked it down to a smaller simpler pattern.


PHP 5.1.0-dev (cli) (built: Jul  6 2005 10:55:39)
Copyright (c) 1997-2005 The PHP Group
Zend Engine v2.1.0-dev, Copyright (c) 1998-2004 Zend Technologies


Reproduce code:
---------------
<?php
preg_match('/(?(?=a) (?R) )/x', 'a', $arr);
preg_match_all('/(?(?=a) (?R) )/x', 'a', $arr);
echo 'fin', "\n";  # will never print
?>

Either preg line will cause the fault.

Expected result:
----------------
Anything but a segmentation fault, some kind of error would be nice.

Actual result:
--------------
Segmentation fault

gdb:
Starting program: /usr/bin/php -f pcrash.php
[Thread debugging using libthread_db enabled]
[New Thread -1211468032 (LWP 22573)]

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread -1211468032 (LWP 22573)]
0xb7f58362 in pcre_compile () from /usr/lib/libpcre.so.3