IterationStateHolder interface for UIData-based components

Current UIData implementation saves only a fey EditableValueHolder attributes between iterations. But some other JSF components have to save some row-related values too. In the standard components set they are UIForm whose attribute "submitted" is row-depended and UIData itself. In the third-party components are Facelets UIRepeat, Tomahawk data tables, some RichFaces components etc. Currently, most of them look for a parent "UIDate" instance to adjust per-row behavior. My proposal is delegate per-iteration state procedures to the IterationStateHolder interface, as StateHolder does for a per request state:

public interface IterationStateHolder {

   public Object saveIterationState(FacesContext context); 

   public void restoreIterationState(FacesContext context, Object state);
}