First, I would *love* to clean up this section of code, and I'm pleased to learn of the existence of `resource#name`. However, I _think_ messing around with the downloaded names might be necessary in this case because the file ending is important. Like, [the `src_ext/Makefile`](https://github.com/ocaml/opam/blob/240edf448162832c42ddc354ebb52ec5aca2a0eb/src_ext/Makefile) looks for (e.g.,) "cmdliner-0.9.3<strong>.tbz</strong>" and "cudf-0.6.3<strong>.tar.gz</strong>" specifically.

I'm open to ideas. One alternative I can think of is altering the Makefile so it will do what we want—would that be preferable?