Original commit message from CVS:
* sys/dshowdecwrapper/gstdshowaudiodec.cpp:
* sys/dshowdecwrapper/gstdshowaudiodec.h:
* sys/dshowdecwrapper/gstdshowfakesrc.cpp:
* sys/dshowdecwrapper/gstdshowutil.cpp:
* sys/dshowdecwrapper/gstdshowutil.h:
* sys/dshowdecwrapper/gstdshowvideodec.cpp:
* sys/dshowdecwrapper/gstdshowvideodec.h:
Prefer known-good filters, create directly by GUID if possible,
fall back to creating highest-merit filter otherwise.
Fixes playback with random dshow filters installed in some
cases.