adding ref to rwi.stats help. Other small changes to that file.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/dplr@741 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
added ref to SNR calc

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/dplr@742 edb9625f-4e0d-4859-8d74-9fd3b1da38cb