input: appletouch: fixes for jagged/uneven cursor movement

The appletouch driver can make some touchpads feel insensitive, with movement that tends to jerk in steps. This is particularly evident when moving diagonally. There is also undesirable movement when additional fingers enter or leave the touchpad.

These patches address these issues by dialing back the fuzz setting, by implementing sensor data smoothing and by discarding movements that directly coincide with a change in the number of fingers detected on the touchpad.

Thanks Clinton, for resolving this long-standing nuisance. It all looks good to
me now.

Henrik