'Move up selected header.'

def _move_header_up(self, widget):

    selection = self._headersTreeview.get_selection()
    (model, selected) = selection.get_selected()
    if (not selected):
        return
    path = model.get_path(selected)
    position = path[(-1)]
    if (position == 0):
        return
    prev_path = list(path)[:(-1)]
    prev_path.append((position - 1))
    prev = model.get_iter(tuple(prev_path))
    model.swap(selected, prev)
    self._changed()
