Fixed PHP-1111: MongoClient constructor crashes on connection to slave.

https://jira.mongodb.org/browse/PHP-1111
What does 'cs' stand for? ClientSlave? o.O
$rs I was expecting replicaset info, but it holds maser/slave info..
I can't clearly tell which one is the master and which is slave.

In any case, could you add $master->findOne() and $secondary->slaveOkay()->findOne() to make sure both works?