Now that we've moved to atomic replacement of these files when altering
them, we don't need to keep them open for the lifetime of Core::Account
so just simplify this and close them when they are not needed.
Before this patch, we had a nasty race condition when changing a user's
password: there was a time window between truncating /etc/shadow and
writing out its new contents, where you could simply "su" to root
without using a password.
Instead of writing directly to /etc/passwd and /etc/shadow, we now
create temporary files in /etc and fill them with the new contents.
Those files are then atomically renamed to /etc/passwd and /etc/shadow.
Sadly, fixing this race requires giving the passwd program a lot more
privileges. This is something we can and should improve upon. :^)
Now, `chres 640 480 2` can set the UI to HighDPI 640x480 at runtime. A
real GUI for changing the display factor will come later.
(`chres 640 480 2` followed by `chres 1280 960` is very fast since
we don't have to re-allocate the framebuffer since both modes use
the exact same number of physical pixels.)
This API was a mostly gratuitous deviation from POSIX that gave up some
portability in exchange for avoiding the occasional strlen().
I don't think that was actually achieving anything valuable, so let's
just chill out and have the same open() API as everyone else. :^)
