Bug 123316 [Undo] - API BEHAVIOR - should always place a successfully undone/redone op on the redo/undo history
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/operations/IOperationHistory.java
* 
	 * @param context
	 *            the context for the redo
	 * @return the operation to be redone or <code>null</code> if there is no
	 *         operation available. There is no guarantee that the returned
	 *         operation is valid for redo.
	 */
	IUndoableOperation getRedoOperation(IUndoContext context);
	/**
	 * <p>
	 * Get the array of operations in the undo history for the specified undo
	 * context. The operations are in the order that they were added to the
	 * history, with the most recently added operation appearing last in the
	 * array. This history is used LIFO (last in, first out) when successive
	 * "Undo" commands are invoked.
	 * </p>
	 * 
	 * @param context
	 *            the context for the undo
	 * @return the array of operations in the history
	 */
	IUndoableOperation[] getUndoHistory(IUndoContext context);
	/**
	 * <p>
	 * Open this composite operation and consider it an operation that contains
	 * other related operations. Consider all operations that are subsequently
	 * executed or added to be part of this operation. When an operation is
	 * opened, listeners will immediately receive a notification for the opened
	 * operation. The specific notification depends on the mode in which the
	 * operation is opened (<code>ABOUT_TO_EXECUTE</code>,