Adding function to chart concentration based on Peter's symposium slides along with a demo

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/returnanalytics@3313 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
minor revisions to risk budget optimization vignette to work with new structure of optimize.portfolio.rebalancing objects

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/returnanalytics@3314 edb9625f-4e0d-4859-8d74-9fd3b1da38cb