Similar to os.walk method. Insted of filesystem it walks through
        changeset starting at given ``topurl``.  Returns generator of tuples
        (topnode, dirnodes, filenodes).

def walk(self, topurl=''):
        """
        Similar to os.walk method. Insted of filesystem it walks through
        changeset starting at given ``topurl``.  Returns generator of tuples
        (topnode, dirnodes, filenodes).
        """
        topnode = self.get_node(topurl)
        yield (topnode, topnode.dirs, topnode.files)
        for dirnode in topnode.dirs:
            for tup in self.walk(dirnode.path):
                yield tup