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/DefaultOperationHistory.java
Assert.isNotNull(context);
		return filter(undoList, context);
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.core.commands.operations.IOperationHistory#getUndoOperation(org.eclipse.core.commands.operations.IUndoContext)
	 */
	public IUndoableOperation getUndoOperation(IUndoContext context) {
		Assert.isNotNull(context);
		synchronized (undoRedoHistoryLock) {
			for (int i = undoList.size() - 1; i >= 0; i--) {
				IUndoableOperation operation = (IUndoableOperation) undoList
						.get(i);
				if (operation.hasContext(context)) {
					return operation;
				}
			}
		}
		return null;
	}
	
	/*
	 * Consult the IOperationApprovers to see if the proposed execution
	 * should be allowed.
	 * 
	 * @since 3.2
	 */
	private IStatus getExecuteApproval(IUndoableOperation operation,
			IAdaptable info) {