Description:
------------
Iteration through a large ArrayObject (e.g. 10,000+ items) is very slow.

Reproduce code:
---------------
$a = new ArrayObject;
for ($i = 0; $i < 10000; $i++) 
    $a[] = $i;

// This is slow
foreach ($a as $k => $v);

// This is much faster, even though I thought this was basically what ArrayObject's getIterator method did.
$it = new ArrayIterator($a->getArrayCopy());
foreach ($it as $k => $v);