docs

git-svn-id: https://svn.r-project.org/ESS/trunk@5498 0bbaf3bd-34e0-0310-bf65-c717079852d4
don't skip "debugging in" references. It always comes with "debug at" in recent R versions.

git-svn-id: https://svn.r-project.org/ESS/trunk@5499 0bbaf3bd-34e0-0310-bf65-c717079852d4