Wraps around container.bind().

def bind(self, func, etype):
        '''
        Wraps around container.bind().
        '''
        if func not in self._event_cbs:
            wrapped = self._WrapCB(self, func)
            self._event_cbs[func] = wrapped
        else:
            wrapped = self._event_cbs[func]
        self.container.bind(wrapped, etype)