Unveil Changes in OpenBSD 6.5


Prior to OpenBSD 6.5, you had to cross an unveil'ed vnode on a name
lookup in order for unveil to work. this was inconvenient when you
wanted to do relative access underneath directory below an unveil.

There was limited support for relative path lookups.

This was fixed in OpenBSD 6.5 so that unveil can always find the
covering unveil above any directory.

 unveil("/", "r") now becomes useful, and we can use it a lot!