Description:
------------
Using =&, it is possible to modify $this with the constructor. 

This shouldn't be allowed, just like for 
$tmp = $this;

Reproduce code:
---------------
<?php

class B {

  function B() {

  }

}

class A {

  function A() {
    $tmp =& $this;
    var_dump($this); // outputs : object(A)
    $tmp = new B();
    var_dump($this); // outputs : object(B)
  }

}

$a = new A();

var_dump($a); // outputs : object(A)

?>


Expected result:
----------------
object(A)#1 (0) {
}
object(A)#2 (0) {
}
object(A)#1 (0) {
}

// current result : 
object(A)#1 (0) {
}
object(B)#2 (0) {
}
object(A)#1 (0) {
}