Can't use phpredis prefix.

config.yml
```yml
snc_redis:
    clients:
        default:
            dsn: "redis://localhost:6379"
            options:
                prefix : "prefix"
            type: phpredis
            alias: default
            logging: %kernel.debug%
```
This setting throws excection follows.

```
RedisException: Redis server went away
in /data/home/soichiro_yoshimura/workspace/trunk/Symfony/app/cache/neat_dev/appNeat_devDebugProjectContainer.php line 2513
at Redis->setOption('2', 'prefix') in /data/home/soichiro_yoshimura/workspace/trunk/Symfony/app/cache/neat_dev/appNeat_devDebugProjectContainer.php line 2513
at appNeat_devDebugProjectContainer->getSncRedis_DefaultService() in /data/home/soichiro_yoshimura/workspace/nicotter/Symfony/app/bootstrap.php.cache line 211
// ...
```

/data/home/soichiro_yoshimura/workspace/trunk/Symfony/app/cache/neat_dev/appNeat_devDebugProjectContainer.php line 2513
```php
/**
 * Gets the 'snc_redis.default' service.
 *
 * This service is shared.
 * This method always returns the same instance of the service.
 *
 * @return Snc\RedisBundle\Client\Phpredis\Client A Snc\RedisBundle\Client\Phpredis\Client instance.
 */
protected function getSncRedis_DefaultService()
{
    $a = new \Redis();
    $a->setOption(2, 'prefix');
    $a->connect('localhost', 6379, 2);
    $a->select(0);

    $this->services['snc_redis.default'] = $instance = new \Snc\RedisBundle\Client\Phpredis\Client(array('alias' => 'default'), $this->get('snc_redis.logger'));

    $instance->setRedis($a);

    return $instance;
}
```

Please fix to move "setOption" after "connect". and test phpredis prefix options.