rem: Handlers.push_back(Handler);
add: handlers.push_back(handler);
context: status_t _ObserverList::StartObserving(BHandler* Handler, unsigned long what){	if (!Handler)	{		return B_BAD_HANDLER;	}	vector<BHandler*>& Handlers = fHandlerMap[what];	vector<BHandler*>::iterator iter;	iter = find(Handlers.begin(), Handlers.end(), Handler);	if (iter != Handlers.end())	{		// TODO: verify		return B_OK;	}	Handlers.push_back(Handler);	return B_OK;}