[Vala] Switch statement on GType.

[Sam Danielson <samdanielson gmail com>]

Under Vala 0.6 the following worked.

switch (tree_store.get_column_type (n)) {
    case typeof(string):
        ...
    break;
}


In Vala 0.7 it does not -- error: Integer or string expression expected.

But GLib.Type derives from ulong so this seems to violate the Liskov
substitution principle. Is this a bug or desired behavior?

-Sam Danielson