Also fixes some issues where nested transactions will poison the
verification cache.

So IDNs are not rejected. Invalid server names will be caught later.

We explicitly set a parent. We can't assign to
ApplicationWindow.transientParent though, only to
Window.transientParent, so we just call setTransientParent in C++.

fixes #636

Co-authored-by: DeepBlueV7.X <nicolas.werner@hotmail.de>