This is a method for the generic function rescale. The spatial coordinates in the point pattern X
(and its window) will be re-expressed
in terms of a new unit of length that is s times the current
unit of length given in X.
(Thus, the coordinate values are divided by s,
while the unit value is multiplied by s).
The result is a point pattern representing the same data
but re-expressed in a different unit.
Mark values are unchanged.