Re: disallowing 'make installworld' with pkgbase

Tomoaki AOKI wrote in <20251006204554.d1ea4dc8671f72e70f678875@dec.sakura.ne.jp>:
> Isn't there at least one edge case with D52879?
> 
> What I can think of is
>   *pkgbase installation,
>   */usr/local/ and /var/db/pkg/ (/var/cache/pkg/, too, possibly?) are
>    NOT in root partition,
>   *running `make installworld` in single user mode,
>   *any of the partitions / datasets that above-mentioned directories
>    exists are NOT mounted.

you need /var and /usr mounted for make installworld to work.  a
situation where /usr is mounted but /usr/local is not is niche enough
that i don't think it matters for this.  the purpose isn't to prevent
every possible user error (which is impossible), only the majority of
them, i.e., the most common case.