[PATCH libinput 00/12] button-scrolling fixes

[Peter Hutterer]

The core bits here are 05/12 and 11/12, the rest is restructuring and
various fixes to enable those two.

05/12 enables button-scrolling on the left/right mouse button when middle
button emulation is also active. This currently works but generates a
log_bug_libinput() because of a negative timer offset. There are some mice
(trackballs, mainly) that only have two buttons so both middle button
emulation and button scrolling on the same device is useful, even though
it's a bit of a niche case.

11/12 extends the button scrolling implementation. Right now, we have three
states: idle, button is down and scrolling. The latter is triggered as soon
as the scroll button is held past the timeout. But that also results in the
button being inconsistent - a short click generates a button click, a long
click (but without scrolling) is discarded. With these fixes, a long click
now sends button events if there never were any scroll events generated.

Cheers,
  Peter