bibclean 2.16 (new formula)

* Build failed with superenv, hence included `env :std`.
* `ENV.deparallelize` was also necessary.
* Two `inreplace` statements insert `mkdir` statements needed on MacOS.
* One `inreplace` statement fixes the `mandir` variable in `Makefile`,
since it is not properly defined by autoconfig despite the `--mandir`
parameter passed to `./configure`.
@mikemcquaid, I'm swamped these days so I might not be able to do that before you. But what's the rationale anyway? The 1-line Shell statement is compact, effective, and readable.