Ticket #5 (closed defect: fixed)

The callgraphs I generated looked wrong. It turns out that the tracer function needs to return a tracer to be used in each local scope! (See http://www.python.org/doc/2.3.4/lib/debugger-hooks.html#debugger-hooks)

I added a line to tracer, to return itself. That seemed to work:

def tracer(frame, event, arg):
    ................
    if event == 'return':
        if pr: print 'return'
        if call_stack:
            call_stack.pop(-1)
    return tracer   #new