minor changes in backtest plot, adding missing function pfolioReturn

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rmetrics@5854 5d4a7380-5c0c-0410-b446-d4a5018c0119
fitting functions updated

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rmetrics@5855 5d4a7380-5c0c-0410-b446-d4a5018c0119