Its very easy to get extra references to the NativeDialog so that
when you release your last reference any visible dialog is not
hidden. We handle this by adding a destroy method similar to how
you destroy regular toplevels.
This is a base class that essentially mirrors GtkDialog, but
it is not a GtkWindow, as the actual implemetation will be using
native code.
The base class has show and hide vfuncs, as well as a helper function
to run the dialog in a modal fashion.
This will be later used by the native file chooser dialog.