Database.current_op does not use CodecOptions when the server is >=3.2

Database.current_op does not use CodecOptions when the server is >=3.2 but does use it on server <= 3.2:
https://github.com/mongodb/mongo-python-driver/blob/3.7.2/pymongo/database.py#L832-L833

This means a user that wants ordered results or to set the unicode_decode_error_handler as in https://groups.google.com/forum/#!topic/mongodb-user/tgXYrTepBWE needs to use Database.command directly.