Bug 156632 [Acceptance]Cannot paste theme when select Themes in Outline.
Description: Cannot paste theme when select Themes in Outline. Steps to reproduce: 1. New a library. 2. Select defaulttheme in outline and cut it 3. Select Themes and right click to paste the theme back. Expected result: Paste in context menu can be used. Actual result: Paste is gray
UI/org.eclipse.birt.report.designer.core/src/org/eclipse/birt/report/designer/util/DNDUtil.java
return (DesignElementHandle) target;
		}
		else if ( target instanceof SlotHandle )
		{
			return ( (SlotHandle) target ).getElementHandle( );
		}
		return null;
	}
	/**
	 * Unwraps the object to model
	 * 
	 * @param obj
	 *            object which may be wrapped, such as
	 *            <code>ReportElementModel</code>, <code>ListBandProxy</code>
	 * @return model object
	 */
	public static Object unwrapToModel( Object obj )
	{
		if ( obj instanceof ReportElementModel )
		{
			return ( (ReportElementModel) obj ).getSlotHandle( );
		}
		if ( obj instanceof ListBandProxy )
		{
			return ( (ListBandProxy) obj ).getSlotHandle( );
		}
		return obj;
	}
	/**
	 * Gets the length of elements in object