Original commit message from CVS:
* configure.ac: OSS portability
* ext/arts/gst_arts.c: idem
* sys/oss/gstosselement.c: idem
* sys/oss/gstossmixer.c: idem
* sys/oss/gstosssink.c: idem
* sys/oss/gstosssrc.c: idem
* sys/oss/oss_probe.c: idem
- check for soundcard.h in different places for some BSD