porting functions/files from xtsExtra to xts for plot.xts

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/xts@866 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
* moving man files from xtsExtra to xts for plot.xts and add* functions

* updating NAMESPACE with appropriate functions and methods for new version of plot.xts


git-svn-id: svn://svn.r-forge.r-project.org/svnroot/xts@867 edb9625f-4e0d-4859-8d74-9fd3b1da38cb