Log Message:
Add stereo/mono fallback logic for `oss' audio output.

Previously playing files with more audio channels available than the ones
provided by audio device resulted in muted audio. A possible workaround to that
was forcing the `--audio-channels=2' or similar.

Thanks to <mrg> for kindly provided a reliable test (file|case) for that!

While here also get rid of a trailing whitespace in options.mk (spotted by
pkglint!)

Bump PKGREVISION.