Description:
------------
This is basically the same as bug 42752 but in the array_merge_recursive rather than the array_walk recursive code. The fix is the same.

The detection of recursion used in array_merge_recursive is incorrect so it is possible to pass recursive arrays that cause unbounded recursion, leading to stack overflow.

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

$a=array("key1"=>array("key2"=>array()));
$a["key1"]["key2"]["key3"]=&$a;

$b=array("key1"=>array("key2"=>array()));
$b["key1"]["key2"]["key3"]=&$b;

array_merge_recursive ($a,$b);
echo "reached the end \n";

?>

Expected result:
----------------
reached the end

Actual result:
--------------
crash