HasStrictTraits class sets dunder values when passed to constructor

Consider this example

```
>>> class Foo(HasStrictTraits):
... a = Int()
>>> Foo(whatever=5)
Traceback (most recent call last):
File "", line 1, in
traits.trait_errors.TraitError: Cannot set the undefined 'whatever' attribute of a 'Foo' object.
>>> x=Foo(__foo__=4)
>>> x.trait_names()
['a', 'trait_added', 'trait_modified', '__foo__']
```

I would expect to refuse it in either case.