Issue #647: Optimisation of flatplot, in particular gridlines

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/retistruct@1276 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Documentation tweaks


git-svn-id: svn://svn.r-forge.r-project.org/svnroot/retistruct@1277 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Issue #647: More plotting optimisation


git-svn-id: svn://svn.r-forge.r-project.org/svnroot/retistruct@1278 edb9625f-4e0d-4859-8d74-9fd3b1da38cb