[py3] fixed session file backend.

from django.conf import settings

from django.contrib.sessions.backends.base import SessionBase, CreateError

from django.core.exceptions import SuspiciousOperation, ImproperlyConfigured

from django.utils.encoding import smart_bytes

class SessionStore(SessionBase):

            renamed = False

            try:

                try:

                    os.write(output_file_fd, self.encode(session_data))

                    os.write(output_file_fd, self.encode(session_data).encode())

                finally:

                    os.close(output_file_fd)

                os.rename(output_file_name, session_file_name)