Description:
------------
Fetching data through dblib causes php memory usage to go up after each query. 
This occurs even after unsetting the retrieved data.

This is because free_rows is not freeing the correct data.

Test script:
---------------
<?php
$db = new PDO('...','...','...');
$stmt = $db->prepare('SELECT TOP 100 * FROM Users');
echo "Start Memory : ".memory_get_peak_usage()."\n";

for ($i = 0; $i < 10; $i++) {

	$stmt->execute();
	$data = $stmt->fetchAll();

	unset($data);
	gc_collect_cycles();	
	echo $i." : ".memory_get_peak_usage()."\n";
}
echo "End Memory : ".memory_get_peak_usage()."\n";

Expected result:
----------------
Memory usage should be similar after each execution

Start Memory : 630824
0 : 1257944
1 : 1258024
2 : 1258920
3 : 1258920
4 : 1258984
5 : 1259048
6 : 1259096
7 : 1259224
8 : 1259288
9 : 1259296
End Memory : 1259296


Actual result:
--------------
Memory usage increases significantly after each execution

Start Memory : 630824
0 : 1257944
1 : 1321216
2 : 1384528
3 : 1447688
4 : 1510920
5 : 1574192
6 : 1637464
7 : 1700736
8 : 1763960
9 : 1827208
End Memory : 1827208