R1:9e3baacc95c2

Restore old "author can not be a reviewer" rule to Transactions

Summary:
This is a bit messy, but not tooo bad:

- In general, stop the author from being added as a reviewer.
- In the specific case that "self accept" is enabled, allow it. This is easier than trying to special case it.
- When commandeering, we make the author a reviewer and make the actor the author, but these happen after validation. At validation time, it looks like we're making the author a reviewer. Just special case this.