+JH/05 Bug 2273: Cutthrough delivery left a window where the received messsage
+ files in the spool were present and unlocked. A queue-runner could spot
+ them, resulting in a duplicate delivery. Fix that by doing the unlock
+ after the unlink. Investigation by Time Stewart. Take the opportunity to
+ add more error-checking on spoofile handling while that code is being
+ messed with.
+