core: explicitly unexport objects when we're done with them

Previously most objects were implicitly unexported when they were
destroyed, but since refcounts may make the object live longer than
intended, we should explicitly unexport them when they should no
longer be present on the bus.

This means we can assume that objects will always be un-exported
already when they are destroyed, *except* when quitting where most
objects will live until exit because NM leaves interfaces up and
running on quit.

src/nm-exported-object.h

@@ -45,6 +45,8 @@ typedef struct {
 
 GType nm_exported_object_get_type (void);
 
+void nm_exported_object_class_set_quitting  (void);
+
 void nm_exported_object_class_add_interface (NMExportedObjectClass *object_class,
                                              GType                  dbus_skeleton_type,
                                              ...) G_GNUC_NULL_TERMINATED;
@@ -56,6 +58,9 @@ void        nm_exported_object_unexport    (NMExportedObject *self);
 GSList *    nm_exported_object_get_interfaces (NMExportedObject *self);
 GDBusInterfaceSkeleton *nm_exported_object_get_interface_by_type (NMExportedObject *self, GType interface_type);
 
+void        _nm_exported_object_clear_and_unexport (NMExportedObject **location);
+#define nm_exported_object_clear_and_unexport(location) _nm_exported_object_clear_and_unexport ((NMExportedObject **) (location))
+
 G_END_DECLS
 
 #endif	/* NM_EXPORTED_OBJECT_H */