message: add back compat for IRegisterOp refEsq
diff: @@ -69,7 +69,7 @@ interface IRegisterOperation<T> {
  // As such, refSeq needs to reference seq # at the time op was created,
  // not when op was actually sent over wire (ISequencedDocumentMessage.referenceSequenceNumber),
  // as client can ingest ops in between.
  - refSeq: number;
  + refSeq: number | undefined;
  }
  const newRegisterOp = <T>(key: string, value: T, serializedValue: string, refSeq: number): IRegisterOperation<T> =>
  @@ -257,6 +257,11 @@ export class ConsensusRegisterCollection<T>
  const op: IRegisterOperation<T> = message.contents;
  switch (op.type) {
  case "write": {
  + // back-compat 0.13 refSeq
  + // when the refSeq property didn't exist
  + if (op.refSeq === undefined) {
  + op.refSeq = message.referenceSequenceNumber;
  + }
  // Message can be delivered with delay - e.g. resubmitted on reconnect.
  // Use the refSeq from when the op was created, not when it was transmitted
  const refSeqWhenCreated = op.refSeq;
  