You have a typo in the defines in the header file...

35 #define THUNAR_IS_CLIPBAORD_MANAGER_CLASS(klass)  (G_TYPE_CHECK_CLASS_TYPE ((klass), THUNAR_TYPE_CLIPBOARD_MANAGER))
36 #define THUNAR_CLIPBOARD_MANAGER_GET_CLASS(obj)   (G_TYPE_INSTANCE_GET_CLASS ((obj), THUNAR_TYPE_CLIPBAORD_MANAGER, ThunarClipboardManagerClass))

I don't know what this breaks, but I guess this is not intentional, so you might consider s/CLIPBAORD/CLIPBAORD/g.