Reimplemented to cancel the hide timer.

def enterEvent(self, event):
        """ Reimplemented to cancel the hide timer.
        """
        super(CallTipWidget, self).enterEvent(event)
        if self.as_tooltip:
            self.hide()

        if (self._hide_timer.isActive() and
          self.app.topLevelAt(QCursor.pos()) == self):
            self._hide_timer.stop()