The main thing in this commit is the new wrapper to plot rwl objects. This is setting the stage for having plot, summary, etc. methods for rwl objects. There are still several things to work on. Like setting the class() of rwl data objects via read.rwl (and in the onboard data sets). And will this class change break any existing functions?

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/dplr@748 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
fixed typo. need to resolve warning when checking S3 generic/method consistency.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/dplr@749 edb9625f-4e0d-4859-8d74-9fd3b1da38cb