Make archiving hooks protected in layout classes.

Furthermore,
* remove a stray blank line in Layout.cpp
* make BLayoutItem::SetLayout() private, as it should have been

headers/os/interface/SplitView.h

@@ -71,13 +71,14 @@ public:
 									// overridden to avoid use
 
 	virtual status_t			Archive(BMessage* into, bool deep = true) const;
-	virtual	status_t			AllArchived(BMessage* into) const;
-	virtual status_t			AllUnarchived(const BMessage* from);
 	static	BArchivable*		Instantiate(BMessage* from);
 
 	virtual	status_t			Perform(perform_code d, void* arg);
 
 protected:
+	virtual	status_t			AllArchived(BMessage* into) const;
+	virtual status_t			AllUnarchived(const BMessage* from);
+
 	virtual	void				DrawSplitter(BRect frame,
 									const BRect& updateRect,
 									enum orientation orientation,