Description:
------------
The array_intersect_ukey() function appears to have an invalid algorithm for 
iterating over array keys to be passed to the user function.  A simple test case 
that implements the same behavior as array_intersect_key() illustrates the bug.

Test script:
---------------
<?php
function func($key1, $key2) {
  if ($key1 == $key2) {
    return 0;
  }
  return 1;
} 

$all = array('cat' => 'brown',
  'dog' => 'yellow',
  'mouse' => 'grey',
  'horse' => 'white'
);

$keep = array('dog' => 1, 'horse' => 1);

// Output of the following should be identical
print_r(array_intersect_key($all, $keep));
print_r(array_intersect_ukey($all, $keep, 'func'));
?>

Expected result:
----------------
Array
(
    [dog] => yellow
    [horse] => white
)
Array
(
    [dog] => yellow
    [horse] => white
)

Actual result:
--------------
Array
(
    [dog] => yellow
    [horse] => white
)
Array
(
)