sys/oss/gstossmixer.*: Refactored to be more like alsamixer.

sys/oss/gstossmixer.*: Refactored to be more like alsamixer.

Original commit message from CVS:
2005-08-23  Andy Wingo  <wingo@pobox.com>

* sys/oss/gstossmixer.h:
* sys/oss/gstossmixer.c: Refactored to be more like alsamixer.

* sys/oss/gstossmixertrack.h:
* sys/oss/gstossmixertrack.c: Split out from gstossmixer.[ch],
like gstalsamixer.

* sys/oss/gstosssrc.c:
* sys/oss/gstosssink.c: Where before we used a gstosselement
object as a helper library, now just call functions from
gstosshelper.

* sys/oss/gstosshelper.h:
* sys/oss/gstosshelper.c: Made a real library. Removed
propertyprobe for now, should add it back later.

* sys/oss/gstosselement.h:
* sys/oss/gstosselement.c: Removed, we don't have a shared base
class.

* sys/oss/gstosshelper.c (gst_oss_helper_probe_caps): Search
higher-to-lower, makes 16 bit appear earlier in the caps, which
makes it preferred.