This way, we won't be hit with BadValue errors if we set it to a value
outside the X device's range. This can happen for touchpads without
two-finger scrolling, for instance.
We'll need to get the value of some properties. Fail if the number of
items returned is less than we expect and warn if it exceeds it so
that we can easily find out if items are added to a property later and
fix it.
There is copy&pasted code in set_scroll_button, which is apparently
wrong, because it is trying to set scroll method instead of the scroll
button...
https://bugzilla.gnome.org/show_bug.cgi?id=747967
This goes through modifying XI2 device properties, either common ones (eg.
set on every device) or those specific to the libinput X11 driver. Keyboard
repeat/rate are set through core and XKB APIs.
https://bugzilla.gnome.org/show_bug.cgi?id=739397
