This allows correct iteration over nested lists.
Also store values to variables without resolving them, to delay the
resolution step as much as possible (this helps with storing nested
lists in variables).
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. :^)
