Support setters that work on references in forms and elements

When passing array of options to constructor (or directly to `setOptions` method) containing references that should be set by setter with reference in it's params definition, references were not preserved.

Better explained by example:

Setter in form class:
```php
public function setFoo(& $foo) {
    $this->_foo =& $foo;
}
```

Then:

```php
$foo = 42;
$form->setFoo($foo);
$foo = 13;
echo $form->getFoo(); // 13

// but

$foo = 42;
$form = new AForm(array('foo' => & $foo));
$foo = 13;
echo $form->getFoo(); // 42
```