Description:
------------
array_merge() changed behavior in PHP7, the reproduce script below produces references, which it didn't do in PHP5.

Test script:
---------------
<?php
$x = 'xxx';
$d = ['test' => &$x];
unset($x);
$a = ['test' => 'yyy'];
$a = array_merge($a, $d);
debug_zval_dump($a);
?>

Expected result:
----------------
array(1) refcount(2){
  ["test"]=>
  string(3) "xxx" refcount(2)
}


Actual result:
--------------
array(1) refcount(2){
  ["test"]=>
  &string(3) "xxx" refcount(1)
}