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/AbstractLayout.h

@@ -37,6 +37,11 @@ public:
 	virtual	void				SetVisible(bool visible);
 
 	virtual status_t			Archive(BMessage* into, bool deep = true) const;
+
+	virtual	status_t			Perform(perform_code d, void* arg);
+
+protected:
+	// Archiving hook methods
 	virtual	status_t 			AllArchived(BMessage* archive) const;
 	virtual	status_t			AllUnarchived(const BMessage* from);
 
@@ -45,9 +50,6 @@ public:
 	virtual	status_t			ItemUnarchived(const BMessage* from,
 									BLayoutItem* item, int32 index);
 
-	virtual	status_t			Perform(perform_code d, void* arg);
-
-protected:
 	virtual	bool				ItemAdded(BLayoutItem* item, int32 atIndex);
 	virtual	void				ItemRemoved(BLayoutItem* item, int32 fromIndex);
 	virtual	void				LayoutInvalidated(bool children);