This is a method for the generic command
contour for the class "imlist".
An object of class "imlist" represents a list of pixel images.
(The outdated class "listof" is also handled.)
Each entry in the list x will be displayed as a contour plot,
in an array of panels laid out on the same graphics display,
using plot.solist. Invididual panels are plotted
by contour.im.