In the current implementation, movements > threshold and timeouts usually move
to HOLD state and continue from there. Where a finger is lifted, we go back
up the diagram into the previous finger count's HOLD state.

The side-effect of this is that a tap of a finger can be counted as tap even
after a movement:

- two fingers down, move to scroll, hold down
- third finger down, third finger up

This sequence triggers an erroneous three-finger tap. Once the motion
threshold is hit by any touch, no finger must trigger 2/3 finger tap events
while any touch is down.

The false tap is only triggered where the new finger can execute a tap without
any other finger changing any property. This can be triggered on the
reporter's Dell Precision 5520 but on most other touchpads, a new finger down
will trigger slight movement, pressure or touch size updates and thus the bug
cannot be triggered.

Fixes #382



Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>