export and document new maxEV type of hhh4 plots

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/surveillance@832 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
- new argument maxEV for summary.hhh4 (defaults to FALSE since it can be slow)
- speed up getMaxEV by taking advantage of matrix structure in specific cases


git-svn-id: svn://svn.r-forge.r-project.org/svnroot/surveillance@833 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
added to NEWS and slimmed the description

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/surveillance@834 edb9625f-4e0d-4859-8d74-9fd3b1da38cb