code: public void ensureIndex(DBObject keys, String name) throws MongoException {
          ensureIndex(keys, name, false);
      }
docs: calls {@link DBCollection#ensureIndex(com.mongodb.DBObject, java.lang.String, boolean)} with unique=false
  
  @param keys fields to use for index
  @param name an identifier for the index
  @throws MongoException If an error occurred