New call tree

Just in case anyone is interested, I have been playing around with a new Call Tree widget, based on graphviz. You can take a look at it by checking out the latest CVS version using BRANCH_GRAPHVIZ as the branch name. I would like to get some feedback on it, which will help me decide whether to use the new widget over the old call tree dialogue.
Naturally, this is still work in progress, so expect a few glitches.