Blender Git Loki

Undo previous changes to sound.

The sound system really needs better design for the sequencer and
patching it up now won't really help us in the long run.

Also the sequencer kept leaking file descriptors when preserving
the audio handlles on undo making the branch unusable on mac and
windows.

It's almost certain patching over this will lead to more trouble, better
handle it separately and keep the system working for now.

Kept threaded loading of waveforms since we control the file input
directly there and leads to nice speedup, but we still clear the whole
sound + the waveform on undo, which is pretty bad.