Description:
------------
Function array_shift() modifies array passed by value from class method.

In the example below $_cache is modified through array_shift() call though $_cache is always passed by value.

The bug doesn't appear if we don't use classes.





Reproduce code:
---------------
class A {
	var $_cache = false;

	function get_array() {
		if (!$this->_cache) $this->_cache = array(1, 2, 3, 4, 5);
		return $this->_cache;
	}
	function get_shifted_array() {
		return array_shift($this->get_array());
	}
}
$a = new A;
for ($i = 0; $i < 5; $i++)
	echo $a->get_shifted_array() . "\n";


Expected result:
----------------
1
1
1
1
1


Actual result:
--------------
1
2
3
4
5