Description:
------------
Add is supported but substract Arrays not

Test script:
---------------
<?php

$foo = array('a' => 1, 'b' => 2);
$bar = array('c' => 3, 'd' => 4);

$foobar = $foo + $bar;
print_r($foobar);

$foo = $foobar - $bar;
print_r($foo);

?>

Expected result:
----------------
Array
(
    [a] => 1
    [b] => 2
    [c] => 3
    [d] => 4
)


Array
(
    [a] => 1
    [b] => 2
)


Actual result:
--------------
Array
(
    [a] => 1
    [b] => 2
    [c] => 3
    [d] => 4
)

Fatal error: Unsupported operand types in array.php on line 9