added SNR to rwi.stats at request of user. modified examples.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/dplr@735 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
fixed plot in rwi.stats example

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/dplr@736 edb9625f-4e0d-4859-8d74-9fd3b1da38cb