Description:
------------
When executing a query that returns a large number of rows (around 16 million) the query() function appears to use a lot more memory than it did in version 5.3.8

I looked through the changelogs and couldn't find any obvious reason why, or any mention of a change in how the function works

Test script:
---------------
<?php
$sql = new mysqli("localhost","username","password");
function checkMemory($key="") {
	$memory = round(memory_get_usage(true) / 1024 / 1024) . "mb";
	echo "Memory " . $key . ": " . $memory . "\n";
}

checkMemory("Before");

$query = "SELECT field1a, field2a, valb1, valb2, valb3, valb4 FROM test.table1
	JOIN test.table2 ON companyb=companya AND field1b=field1a
	WHERE companya='TEST'";
$result = $sql->query($query);

checkMemory("After");

$field = $result->fetch_field();
echo "End\n";

Expected result:
----------------
user@server:~$ /usr/local/php-5.3.8/bin/php memory.php 
Memory Before: 1mb
Memory After: 1mb
End

Actual result:
--------------
user@server:~$ /usr/local/php-5.5.4/bin/php memory.php 
Memory Before: 0mb
Memory After: 427mb
PHP Fatal error:  Out of memory (allocated 1603796992) (tried to allocate 20 bytes) in /home/user/memory.php on line 17