bug 1092231 - fix traits to work with Symbols

I think this is misleading  name, specially since we do have `Object.keys`, how about something like:

```js
const getMemberNames = (object, options={keys:true, names:false, symbols:false}) => {
  const symbols = options.symbols && Object.getOwnPropertySymbols(object);
  const names = options.names ? Object.getOwnPropertyNames(object) :
                options.keys ? Object.keys(object) :
                null;
  
  return symbols && names ? [...names, ...symbols] :
         symbols ? symbols :
         names;
}
```

That way caller can configure what to include and what to exclude & name is less confusing.