With the normal `setup.py`, the installation of the `ossaudiodev`
module is skipped under GNU/Linux with newer kernel versions because
Python 3.1 appends the major kernel version to the result of
`build_ext.get_platform` and later `ossaudiodev` is skipped if the
major kernel version is not 2. A similar problem might occur if
installing in FreeBSD.
This problem may even occur if installing Python 3.1 in a Docker image
of an old OS (e.g. prehistoric Debian or CentOS), because the major
kernel version is still the one of the host system.
The solution is to use `str.startswith` and only check that the
platform starts with 'linux' or 'freebsd'.
