Fixes

 - Forward return code for `utimens` and `rename`.
 - Restore compatibility with old fusepy implementations that implement `create` with only 2 arguments.
 - If FUSE 2 flag_nullpath_ok and flag_nopath members exist, then enable fuse_config.nullpath_ok in FUSE 3.
 - Handle possible null path in all methods mentioned in nullpath_ok documentation.