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/Layout.h

@@ -60,9 +60,12 @@ public:
 			BRect				LayoutArea();
 			BLayoutContext*		LayoutContext() const;
 
-	// Archiving methods
-
 	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);
 
@@ -70,10 +73,6 @@ public:
 									int32 index) const;
 	virtual	status_t			ItemUnarchived(const BMessage* from,
 									BLayoutItem* item, int32 index);
-
-	virtual status_t			Perform(perform_code d, void* arg);
-
-protected:
 	// BLayout hook methods
 	virtual	bool				ItemAdded(BLayoutItem* item, int32 atIndex);
 	virtual	void				ItemRemoved(BLayoutItem* item, int32 fromIndex);