'Handle scrollbar\'s "value-changed" signal.
Figure out if the scroll should be frozen. If the adjustment\'s value
is not in the last page\'s range => means it was moved up =>
the scroll bar should be stopped.'

def scroll_changed(self, vscrollbar):

    adj = vscrollbar.get_adjustment()
    self.freeze_scrollbar = (False if (adj.value >= (adj.upper - adj.page_size)) else True)
