Replies from the user don't have original timestamp

[jrubenoff]

Steps to Reproduce

1. Reply to a long thread in a Github issue.
2. Some time later, move the Github issue to a new repo.
3. Your latest reply isn't prepended with your last comment's timestamp, so it looks like you just commented.

For anyone who's receiving email notifications for the destination repo, this can create a false sense of urgency.

Expected behavior.

All comments in a moved issue should be prepended with their original timestamp.