If I perform a findAndModify query on a replicaset, and a readConcern is set "majority" on instantiation of the MongoClient, an exception is thrown: "Command does not support non local read concern".

Steps to reproduce:

$mongoClient = new \MongoClient("mongodb://127.0.0.1:27019,127.0.0.1:27020,127.0.0.1:27021/?readConcernLevel=majority");
        $collection = $mongoClient->testdb->user;
        $collection->findAndModify(
            array('_id' => new MongoId('55d445973e019c996c78b08e')),
            array('$set' => array('test' => 'success'))
        );

The mongoDB function "findAndModify" supports only "local" readConcerns. However, the mongo-php-library uses the readConcern from the server string in the constructor in the MongoClient class.