With this commit preliminary audio support in VirtualBox is enabled.
The backend supports playback as well as recording sounds from within
a guest VM. Depending on how the guest configures the device model
the audio output may sound disorted. If the guest uses buffers that
are too small, i.e., 10 ms or less, frequent buffer underruns will
occure.
To get this low-latency one has also to increase vbox' update hz
to 200 (i.e., 5ms).
Fixes#1647.
