SELFAUTOPARENT for redistributors

[Karl Berry]

        chomp(my $TLMaster = `kpsewhich -var-value=SELFAUTOPARENT`); # TL root

I believe if you use -var-value=TEXMFROOT, as Johannes suggested, it
will just work without needing to change anything. With native TL the
values will be the same.

$ kpsewhich -var-value SELFAUTOPARENT
/usr/local/texlive/2020
$ kpsewhich -var-value TEXMFROOT
/usr/local/texlive/2020

    chomp(my $TMDIST = `kpsewhich -var-value=TEXMFDIST`); # texmf-dist tree

TEXMFDIST is fine too, of course.

I don't know what works with MiKTeX, but I guess if no one's reporting
any bugs, it doesn't matter. --best, karl.