Hi Guix!

This patch lets you import opam packages from a local file. This is a
feature that was requested a few times, and there it is :)

Now, if you have an OCaml package sources that provides an opam file
(usually called opam, or with the .opam extension), you can import the
package, recursively or not with something like:

guix import opam foo -f foo.opam -r

instead of fetching foo from the repositories, it will fetch the data
directly from the given file. WDYT?