Clutter discards any motion event if next event happens to also be a
motion event. This is problematic when the motion event carries
relative motion deltas, since the information about them is completely
lost.
Until we have moved away made the stage stop discarding motion events,
lets work around the issue by compressing them, effectively adding
multiple relative motion deltas together, would one be discarded.
https://bugzilla.gnome.org/show_bug.cgi?id=771049
This function call only applies to tablets, and thus will error
out unless it's called with CLUTTER_TABLET_DEVICEs. This will
allow setting absolute/relative mapping on those on the fly, as
this is optional.
This will only be practical for pads (and maybe generic buttonsets in
the future?), we just need to know the number as the events will also
contain a number as the identificator.
