HHVM-163: Make sure the new changes also compile under HHVM 3.9 and 3.10
HHVM-163: Make sure the new changes also compile under HHVM 3.9 and 3.10

jmikola/mongo-hhvm-driver-prototype,mongodb-labs/mongo-hhvm-driver,mongodb-labs/mongo-hhvm-driver,jmikola/mongo-hhvm-driver-prototype,mongodb/mongo-hhvm-driver,10gen-labs/mongo-hhvm-driver-prototype,mongodb-labs/mongo-hhvm-driver,10gen-labs/mongo-hhvm-driver-prototype,jmikola/mongo-hhvm-driver,mongodb/mongo-hhvm-driver,jmikola/mongo-hhvm-driver-prototype,mongodb/mongo-hhvm-driver,jmikola/mongo-hhvm-driver-prototype,mongodb-labs/mongo-hhvm-driver,jmikola/mongo-hhvm-driver,mongodb-labs/mongo-hhvm-driver-prototype,10gen-labs/mongo-hhvm-driver-prototype,mongodb-labs/mongo-hhvm-driver-prototype,mongodb/mongo-hhvm-driver,10gen-labs/mongo-hhvm-driver-prototype,jmikola/mongo-hhvm-driver,mongodb-labs/mongo-hhvm-driver-prototype,jmikola/mongo-hhvm-driver,mongodb-labs/mongo-hhvm-driver-prototype