Description:
------------
Output buffering gets segmentation fault

Reproduce code:
---------------
<?php
function ob_bug($buf)
{
        $full_buf = ob_get_clean();
        return $full_buf;
}

ob_start("ob_bug");

echo "test";
exit();
?>


Expected result:
----------------
$full_buf and $buf contains buffer

Actual result:
--------------
(gdb) run -q ob_bug.php
The program being debugged has been started already.
Start it from the beginning? (y or n) y
Starting program: /usr/bin/php -q ob_bug.php
[New Thread 16384 (LWP 1860)]

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 16384 (LWP 1860)]
0x08255a92 in _zend_mm_alloc_int (heap=0x8534208, size=32) at /usr/src/websvr/php-5.2.1/Zend/zend_alloc.c:1497
1497                            zend_mm_add_to_free_list(heap, new_free_block);
(gdb) run -q ob_bug.php
The program being debugged has been started already.
Start it from the beginning? (y or n) y
Starting program: /usr/bin/php -q ob_bug.php
[New Thread 16384 (LWP 1873)]

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 16384 (LWP 1873)]
0x08256565 in _emalloc (size=16) at /usr/src/websvr/php-5.2.1/Zend/zend_alloc.c:1866
1866            return _zend_mm_alloc_int(AG(mm_heap), size ZEND_FILE_LINE_RELAY_CC ZEND_FILE_LINE_ORIG_RELAY_CC);
(gdb) run -q ob_bug.php
The program being debugged has been started already.
Start it from the beginning? (y or n) y
Starting program: /usr/bin/php -q ob_bug.php
[New Thread 16384 (LWP 1875)]

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 16384 (LWP 1875)]
zend_call_function (fci=0xbfd01080, fci_cache=0x0) at /usr/src/websvr/php-5.2.1/Zend/zend_execute_API.c:615
615             zend_class_entry *calling_scope = NULL;