Rollback throwing connection reuse issue after SQL error, is this ok?

[cretz]

Basically, I'm getting "Attempting to reuse a connection in an invalid state. Did you forget a 'done' somewhere?" on InTransaction::rollbackTransaction. This is because it's already out of that state. Do we ask the caller to know that an exception in transaction changes its state? At the very least, document the situation and put some unit tests around it.