Reverting merges is going to be hard without implementing a full VCS backend. But then what
happens to the RDBMS? This case should be rare. So I think the right thing to do is make "Make
a copy" work.
1. Superseded issues should actually become part of the superseding
issue in many cases. Does this happen? If not think about making
it so.
2. When multiple issues are superseded, they should become a single issue.