Bug 156865 Undo / Redo marker actions not updated
I20060906-1200 If a file gets delete after adding/changing/removing a marker then the Undo and Redo actions are not updated and still show, e.g. Undo Add Task Redo Add Task Executing the undo or redo does nothing (no feedback, no .log entry) and the undo and redo menu text remains the same and enabled.
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/ide/undo/AbstractWorkspaceOperation.java
*/
	public void aboutToNotify(OperationHistoryEvent event) {
		
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.core.commands.operations.IAdvancedUndoableOperation#getAffectedObjects()
	 */
	public Object[] getAffectedObjects() {
		return resources;
	}
	/*
	 * Return a status indicating the projected outcome of undoing the receiver.
	 * 
	 * This method computes the validity of an undo by computing the resource
	 * delta that would be generated on undo, and checking whether any
	 * registered model providers are affected by the operation. This method is
	 * not called by the operation history, but instead is used by clients (such
	 * as implementers of {@link IOperationApprover}) who wish to perform
	 * advanced validation of an operation before attempting to undo it. If the
	 * undo is not valid, then the validity flag on the operation should be
	 * marked invalid.
	 * 
	 * @see org.eclipse.core.commands.operations.IAdvancedUndoableOperation#computeUndoableStatus(org.eclipse.core.runtime.IProgressMonitor)
	 */
	public IStatus computeUndoableStatus(IProgressMonitor monitor) {
		IStatus status = Status.OK_STATUS;
		IResourceChangeDescriptionFactory factory = ResourceChangeValidator
				.getValidator().createDeltaFactory();