can't set HISTFILE to /dev/null

[Danek Duvall <duvall@xxxxxxxxxxxxxx>]

A colleague of mine saw this today:

    zsh: locking failed for /dev/null: operation not supported: reading anyway

Turns out he was setting HISTFILE=/dev/null, rather than unsetting it.
4.3.10 was silent in this case, but 4.3.12 now complains.  Is this
intentional?

I've not seen the ENOTSUP, but he was doing something with zones that might
have changed the situation a bit.  Still, if I do

    HISTFILE=/dev/null
    fc -R

then I see

    zsh: locking failed for /dev/null: permission denied: reading anyway

and it appears to be coming from the same place in the code.

Thanks,
Danek