constructor of "simulate" function for isotropic siaf's with given intrfr


git-svn-id: svn://svn.r-forge.r-project.org/svnroot/surveillance@708 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
use polyCub.iso() in siaf.powerlaw()


git-svn-id: svn://svn.r-forge.r-project.org/svnroot/surveillance@709 edb9625f-4e0d-4859-8d74-9fd3b1da38cb