for any reason other than ENOENT (think resource limits). Close allow and
deny files before allowed() returns to stop the user's EDITOR being able to
read them.
Obtained from: OpenBSD (partially)
This will make a number of things easier in the future, as well as (finally!)
avoiding the Id-smashing problem which has plagued developers for so long.
Boy, I'm glad we're not using sup anymore. This update would have been
insane otherwise.