With this option, 'cabal get' writes to the destination directory only the
package description already available locally in one of the repository
indices.

The basename of the file name written to inside the target directory is
the package-id rather than only the package name.

This is mostly based on #1977

Co-authored-by: Miëtek Bak <mietek@bak.io>
Co-authored-by: Artem Pelenitsyn <a.pelenitsyn@gmail.com>

Co-authored-by: Herbert Valerio Riedel <hvr@gnu.org>
Co-authored-by: Miëtek Bak <mietek@bak.io>