OSS4 supports per-stream volume control, so expose this using the right API, so that playbin2 and applications like totem can make use of it (instead of using a volume element for volume control). Fixes #614305.
Original commit message from CVS: * configure.ac: * sys/Makefile.am: * sys/oss4/Makefile.am: * sys/oss4/oss4-audio.c: * sys/oss4/oss4-audio.h: * sys/oss4/oss4-mixer-enum.c: * sys/oss4/oss4-mixer-enum.h: * sys/oss4/oss4-mixer-slider.c: * sys/oss4/oss4-mixer-slider.h: * sys/oss4/oss4-mixer-switch.c: * sys/oss4/oss4-mixer-switch.h: * sys/oss4/oss4-mixer.c: * sys/oss4/oss4-mixer.h: * sys/oss4/oss4-property-probe.c: * sys/oss4/oss4-property-probe.h: * sys/oss4/oss4-sink.c: * sys/oss4/oss4-sink.h: * sys/oss4/oss4-soundcard.h: * sys/oss4/oss4-source.c: * sys/oss4/oss4-source.h: Add initial support for OSSv4. Mixer still needs a bit more love, but even magic has its limits.