Bug 89020 [Undo] Operation throws assertion failure if undo limit is set to 0
I20050324-0800 Unfortunately existing clients of text's undo manager were allowed to set any number without failing. This is no longer possible: an assertion failure occurrs if the limit is smaller than 1. I will add code on my side that will handle the negative numbers but the operation history must allow 0.
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/operations/DefaultOperationHistory.java
*/
	public static final IStatus OPERATION_INVALID_STATUS = new OperationStatus(
			IStatus.ERROR, OperationStatus.OPERATION_INVALID,
			"Operation is not valid"); 
	/**
	 * the list of {@link IOperationApprover}s
	 */
	protected List approvers = new ArrayList();
	/**
	 * a map of undo limits per context
	 */
	private HashMap limits = new HashMap();
	/**
	 * the list of {@link IOperationHistoryListener}s
	 */
	protected List listeners = new ArrayList();
	/**
	 * the list of operations available for redo, LIFO
	 */
	private List redoList = new ArrayList();
	/**
	 * the list of operations available for undo, LIFO
	 */
	private List undoList = new ArrayList();
	
	/**
	 * An operation that is "absorbing" all other operations while
	 * it is open.  When this is not null, other operations added or
	 * executed are added to this composite. 
	 *