ScintillaGTK: Call superclass finalize() in ScintillaObject
The ScintillaObject class does not chain up to its superclass in the finalize()
function. This is a bug and must be done according to the GLib/GObject
documentation. One effect of this is that the destroy notifiers supplied in
e.g. g_object_set_data_full() are never run.
Fixes Bug: #1549 ScintillaObject.finalize() does not chain up