better treatment of source refs from indirect buffers

git-svn-id: https://svn.r-project.org/ESS/trunk@5602 0bbaf3bd-34e0-0310-bf65-c717079852d4
add ess-tracebug-original-buffer-marker

    Useful for applications that use indirect temporary buffers, like org-babel.

git-svn-id: https://svn.r-project.org/ESS/trunk@5603 0bbaf3bd-34e0-0310-bf65-c717079852d4
recognize org-babel-tangled-file

git-svn-id: https://svn.r-project.org/ESS/trunk@5604 0bbaf3bd-34e0-0310-bf65-c717079852d4