PHPLIB-417: countDocuments should use group with _id: 1
PHPLIB-417: countDocuments should use group with _id: 1

mongodb/mongo-php-library,jmikola/mongo-php-library,10gen-labs/mongo-php-library-prototype,mongodb/mongo-php-library,jmikola/mongo-php-library,mongodb/mongo-php-library,jmikola/mongo-php-library,mongodb/mongo-php-library,jmikola/mongo-php-library-prototype,jmikola/mongo-php-library