More tools for 'imlist' and bugfixes.

   plot.listof.R -> plot.anylist.R
   plot.listof.Rd -> plot.anylist.Rd
   contour.listof.Rd -> contour.imlist.Rd
   plot.imlist.Rd [New file]
      New functions plot.imlist, contour.imlist, image.imlist.
      Reorganised functions plot.anylist, plot.solist.

   plot.anylist.R
      Bug fix in handling the legacy case
      ('listof' object consisting of spatial objects)

   vignettes/datasets.Rnw
      Added a plot and description of each dataset.

   demo/data.R
      Fixed a quirk.

   DESCRIPTION
   NEWS
      updated.