Consistent handling of USB device buttons

[Alex Dubov]

> 

> use XI2 and deviceid in events, then you know that the volume up was hit on
> this particular device. clients may not make use of this right now, but the
> infrastructure is in place.

Thanks a lot.
This is exactly the piece of information I was looking for.

> 
> 
> file this as bug and attach an evemu recording, I'll have a look at it.
> http://people.freedesktop.org/~whot/evemu/

Yep, created

https://bugs.freedesktop.org/show_bug.cgi?id=53907

Regards,
Alex