Sync vignette with code, small bug fix for access with names via [[


git-svn-id: svn://svn.r-forge.r-project.org/svnroot/tm@1342 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Sync extensions vignette with code

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/tm@1343 edb9625f-4e0d-4859-8d74-9fd3b1da38cb