Description:
------------
dmitry introduced the new get_gc handler, but seems splfixedarray doesn't 
implement it.

                         
also there are some other extensions still using ugly implementation for gc, I 
will review them one by one.

thanks

Test script:
---------------
<?php
function dummy() {
    $a = new SplFixedArray(1);
    $b = new SplFixedArray(1);
    $a[0] = $b;
    $b[0] = $a;
}

dummy();
var_dump(gc_collect_cycles());

Expected result:
----------------
int(2)

Actual result:
--------------
int(0)