Description:
------------
MemcachePool::getextendedstats() causes PHP notice

PHP 5.3.3
memcache 3.0.5
memcached 1.4.5
Cent OS 5.5

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

$memcache = new Memcache;
$memcache->connect('127.0.0.1', 11211);
$memcache->set('test_key1', '1', 0, 5);
$memcache->set('test_key2', '1', 0, 5);

foreach ($memcache->getExtendedStats('slabs') as $server => $slabs)
    foreach (array_keys($slabs) as $slabId) 
        $memcache->getExtendedStats('cachedump', (int) $slabId);


Expected result:
----------------
scripts runs without any notices

Actual result:
--------------
PHP Notice:  MemcachePool::getextendedstats(): Server 127.0.0.1 (tcp 11211, udp 0) failed with: CLIENT_ERROR bad command line
 (0) in /projects/mongodb_odm/lib/vendor/doctrine-common/tests/Doctrine/Tests/Common/Cache/memcache_bug.php on line 9