Make tap detection less restrictive for multi-finger taps.

Make tap detection less restrictive for multi-finger taps.

In order to distinguish tap gestures from short movements, the mechanism
checks whether the distance between the first and the last position of a
touch exceeds the 'maxdist' limit.  Some touchpads provide unreliable
coordinates when more than one contact is being made simultaneously, and
in this case the filter may be too strong - and superfluous, because only
one-finger contacts should trigger pointer movement.