MenuField: Open the menu bar when the label is clicked

Fixes #6894

Private DrawLabel() method renamed to _DrawLabel() and rest of drawing
code moved to new private method _DrawMenuField(). These methods both
check to make sure that they are drawing in a valid rect that intersects
updateRect.

When label or menu is selected Draw a the label background in the selected
menu color matching the behavior of BeOS R5.

_DrawLabel() calls be_control_look->DrawLabel()

Update copyright year in MenuField.h

headers/os/interface/MenuField.h

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2011, Haiku, Inc. All rights reserved.
+ * Copyright 2006-2013, Haiku, Inc. All rights reserved.
  * Distributed under the terms of the MIT License.
  */
 #ifndef _MENU_FIELD_H
@@ -121,9 +121,12 @@ private:
 								BMenuField(const char* label,
 									BMenu* menu, BMessage* message);
 
+			void				_DrawLabel(BRect updateRect);
+			void				_DrawMenuBar(BRect updateRect);
+
 			void				InitObject(const char* label);
 			void				InitObject2();
-			void				DrawLabel(BRect updateRect);
+
 	static	void				InitMenu(BMenu* menu);
 
 			int32				_MenuTask();