Upon reading the man page properly, I realized that .zshenv decides
what should be loaded how.

This obsoletes my old hack to make it work, and also disables the
global configuration, which puts an end to the annoying .zcompdump
files.

Technically not really standard, but it seems mutt is the only
application using this anyway.

It also supports `$MAILCAPS`, which hopefully other applications will
be happy to adopt if I ever start using them.

I still stand by the fact that this is horrible, but hey, at least I
now mostly use Firefox, so the fallback makes sense in my case...

Still `echo "No application registered for this file type"` would make
so much more sense.

It seems all shells use this file to dump their histories in. This'll
probably cause breakage, but it's better than having a
`~/.bash_history` appear every time I launch a limited dev shell.