Description:
------------
PHP 5 acts as expected, PHP 7 fails.

Test script:
---------------
<?php

$post_data_1 = [ 'file' => new CURLFile('file.txt') ];
$curl_1 = curl_init();
curl_setopt($curl_1, CURLOPT_POSTFIELDS, $post_data_1);
echo "OK\n";

// exactly the same as above + added a reference to 'file' element
$post_data_2 = [ 'file' => new CURLFile('file.txt') ];
$ref = & $post_data_2['file']; // ***
$curl_2 = curl_init();
curl_setopt($curl_2, CURLOPT_POSTFIELDS, $post_data_2);
echo "OK\n";


Expected result:
----------------
PHP 5:

OK
OK


PHP 7:

OK
OK


Actual result:
--------------
PHP 5:

OK
OK


PHP 7:

OK
Catchable fatal error: Object of class CURLFile could not be converted to string in wtf.php on line 12