<b32> Error message when intentionally aborting automatic backup on application exit

Previously Scrivener merely closed cleanly when one clicked Cancel on the auto-backup pop-up.

Now we get a message stating that the backup file could not be created, and the user must clock Ok to close it.
This is both annoying, adds nothing useful, and it’s wrong, as the backup could be created, but the user choose to abort it.

I hope this is not intentional (i.e., to bring it into line with Mac functionality)