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
*/
	private ICompositeOperation openComposite = null;
	
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.core.commands.operations.IOperationHistory#add(org.eclipse.core.commands.operations.IUndoableOperation)
	 */
	public void add(IUndoableOperation operation) {
		Assert.isNotNull(operation);
		
		/*
		 * If we are in the middle of executing an open batching operation, and this is not that
		 * operation, then we need only add the context of the new operation to the batch.  
		 * The operation itself is disposed since we will never undo or redo it.  We consider
		 * it to be triggered by the batching operation and assume that its undo will be triggered
		 * by the batching operation undo.  
		 */
		if (openComposite != null && openComposite != operation) {
			openComposite.add(operation);
			return;
		}
		
		checkUndoLimit(operation);
		undoList.add(operation);
		notifyAdd(operation);
		
		
		IUndoContext[] contexts = operation.getContexts();
		for (int i = 0; i < contexts.length; i++) {