adjust tracebug docs

git-svn-id: https://svn.r-project.org/ESS/trunk@5510 0bbaf3bd-34e0-0310-bf65-c717079852d4
make menus behave well with dead processes

git-svn-id: https://svn.r-project.org/ESS/trunk@5511 0bbaf3bd-34e0-0310-bf65-c717079852d4