Description:
------------
positive lookbehind is causing seg fault in preg_match_all, If i take out the positive lookbehind, it doesn't crash.

Reproduce code:
---------------
<?php
echo "starting\n";
$subject = "enum('active','inactive','rockin\'')";
$pattern = "/'(([^']*((?<=\\\\)')?)*)'/";
preg_match_all($pattern,$subject ,$matches);
print_r($matches);
echo "done.";

Expected result:
----------------
starting
Array
(
    [0] => Array
        (
            [0] => 'active'
            [1] => 'inactive'
            [2] => 'rockin\''
        )

    [1] => Array
        (
            [0] => active
            [1] => inactive
            [2] => rockin\'
        )

    [2] => Array
        (
            [0] => 
            [1] => 
            [2] => 
        )

    [3] => Array
        (
            [0] => 
            [1] => 
            [2] => '
        )

)
done.

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