[metapost] New MPlib beta

[Karl Berry]

    I don't know if that was ever the case in web2c.

I seem to recall that, in the earliest kpathsea/web2c distributions, we
did not use $0, instead relying on the Makefiles to build the fmt files.
(tetex did not exist yet, let alone TeX Live.)  The executables were
shell scripts that executed virtex \&plain "$@" and the like.

I remember being surprised the first time tex wanted tex.fmt instead of
plain.fmt, probably some two decades ago by now.

Historically yours,
karl