[bug#68405] [PATCH v2] guix: download: Add support for git repositories.

["Ludovic Courtès" <ludovic.courtes@inria.fr>]

Hello!

Romain GARBAGE <romain.garbage@inria.fr> skribis:

> * guix/scripts/download.scm (git-download-to-store*): Add new variable.
>   (copy-recursively-without-dot-git): New variable.
>   (git-download-to-file): Add new variable.
>   (show-help): Add 'git', 'commit', 'branch' and 'recursive'options
>   help message.
>   (%default-options): Add default value for 'git-reference' and
>   'recursive' options.
>   (%options): Add 'git', 'commit', 'branch' and 'recursive' command
>   line options.
>   (guix-download) [hash]: Compute hash with 'file-hash*' instead of
>   'port-hash' from (gcrypt hash) module. This allows us to compute
>   hashes for directories.
> * doc/guix.texi (Invoking guix-download): Add @item entries for
>   `git', `commit', `branch' and `recursive' options. Add a paragraph in
>   the introduction.
> * tests/guix-download.sh: New tests.

Full disclosure: Romain and I work together at Inria.  I’ve reviewed the
changes and they LGTM, but we’ll leave time for others to chime in.

Ludo’.