An attempt to pass a Path object as a filename results in a TypeError:
"Must be bytes, not PosixPath". A simple way to accept Path objects
would be unconditionally turning them into strings, but since native
paths may be bytes as well, this might break applications relying on
being able to bytes-based filename. Instead, convert the path into an
appropriate representation (string or bytes) using os.fspath(). It
internally tests whether the path is a PathLike object and does the
right thing.

Signed-off-by: Andrej Shadura <andrew.shadura@collabora.co.uk>