Description:
------------
Attempting to set a subclass' private property in __set causes PHP 5.1.6 (and Apache 2.2.3 using XAMPP 1.5.4) to crash.

Reproduce code:
---------------
class CrashParent {
	public function __set($propertyName, $value) {
		$this->$propertyName = $value;
	}
}

class CrashChild extends CrashParent {
	private $a_property;
}

$instance = new CrashChild();

// Crash here:
$instance->a_property = "a new value";


Expected result:
----------------
Not sure. Either an error indicating you may not set a subclass' private property or preferably the property to be set.

Actual result:
--------------
Crash.