message: Forward original clientId in merged messages
  This gives better presence information
diff: @@ -238,7 +238,7 @@ export class TakeANumber {
  // A merge message contains the sequencing information in the target branch's (i.e. this)
  // coordinate space. But contains the original message in the contents.
  const transformed: core.IRawOperationMessage = {
  - clientId: getBranchClientId(branchOperation.documentId),
  + clientId: branchDocumentMessage.clientId,
  documentId: this.documentId,
  operation: {
  clientSequenceNumber: branchDocumentMessage.sequenceNumber,
  