[ltp] T420s volume controls

[David Woodfall]

I notice that when I upgraded from my T42 to a T420s the volume and
mute keys generate Xorg key events. This would be great but I prefer
it to do hardware mixing, same as my old T42.

Is there any way of doing this? I did try cancelling the keys in
xmodmap, but this doesn't make them work in hardware.

The problem is that most apps don't seem to recognise the xorg events
- chromium browser using flash, mplayer (though I gather I can set
  these keys in its config).