Fix breakage from 1.159. There are actually two methods of supporting
wheeled mice. One is to have moused perform the Z Axis -> Button mapping
and the second is to have the X server perform the mapping. 1.159 added
an example for X 4 for the second method to the section describing the
first method. This fixes this by moving that example to the section on the
second method and adding a new example for X 4 in the section on the first
method. It also fixes a bug in the example for the second method.

Reported by: Hans Lambermont <hans@lambermont.dyndns.org>