Bug 94400 [Undo] - After successful undo, should operation be disposed by framework if it cannot be redone?
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/operations/DefaultOperationHistory.java
IUndoContext[] contexts = operation.getContexts();
			for (int i = 0; i < contexts.length; i++) {
				flushRedo(contexts[i]);
			}
		}
	}
	/**
	 * <p>
	 * Add the specified approver to the list of operation approvers consulted
	 * by the operation history before an undo or redo is allowed to proceed.
	 * This method has no effect if the instance being added is already in the
	 * list.
	 * </p>
	 * <p>
	 * Operation approvers must be prepared to receive these the operation
	 * approval messages from a background thread. Any UI access occurring
	 * inside the implementation must be properly synchronized using the
	 * techniques specified by the client's widget library.
	 * </p>
	 * 
	 * @param approver
	 *            the IOperationApprover to be added as an approver.
	 * 
	 */
	public void addOperationApprover(IOperationApprover approver) {
		approvers.add(approver);
	}
	/**
	 * <p>
	 * Add the specified listener to the list of operation history listeners