Speeding up type checks for final types (commit 0ddea2d8) breaks C++ bindings
Commit 0ddea2d8 (Speed up type checks for final types) causes problems for the C++ bindings (glibmm, gtkmm, etc.).
In the C++ bindings, classes are actually derived from final classes. For instance, a gtkmm__GListStore is derived from GListStore.
I understand that this is probably not what the glib maintainers have intended language bindings to do, but it has worked well up to now. Every C class, derived from GObject, is the parent of another class. gtkmm__GSomeClass is derived from GSomeClass, whether GSomeClass is final or not.
If this commit is included in the next glib release, that release can't be used together with any existing glibmm or gtkmm release.