implemented efficient isotropic cubature for the lagged power law


git-svn-id: svn://svn.r-forge.r-project.org/svnroot/surveillance@773 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
more siaf tests also using polyCub:::checkintrfr()

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/surveillance@774 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
added tests for tiaf.step(); updated NEWS

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/surveillance@775 edb9625f-4e0d-4859-8d74-9fd3b1da38cb