added "nonlocal euid" - without this, euid just gets redefined in inner scope instead of assigned to outer scope
added check for euid 0 - if we run as root, we always have permissions (not just if we are file owner)

note: due to caching and OS behaviour on linux, the bug was a bit tricky to reproduce
and also the fix was a bit tricky to test.

one needs strictatime mount option to enfore traditional atime updating.

for repeated tests, always change file contents (e.g. from /dev/urandom) or attic's caching
will prevent that the file gets read ("accessed") again.

check atimes with ls -lu

i could reproduce code was broken and is fixed with this changeset. and root now doesn't touch any atimes.