Added arithmetic for images and fixed bugs.

   mpl.R
     Fixed bug arising when 'precomputed' data is used
     with skip.border=TRUE. (Bug affected profilepl).

   profilepl.R
     Fixed bug in scoping of external covariates.

   pairorient.R
     Ege's corrections to function labels.

   images.R
   spatstat-internal.Rd
     Ege's fix to [<-.im

   Math.im.R [New file]
   Math.im.Rd [New file]
     Arithmetic for images.

   NEWS
   DESCRIPTION
   spatstat-package.Rd
      Updated and acknowledged Andrew Lister.