* guix/import/elpa.scm (default-files-spec): New variable.
(download-git-repository, package-name->melpa-recipe, file-hash, vcs-file?,
git-repository->origin, melpa-recipe->origin, melpa-recipe->maybe-arguments):
New procedures.
(elpa-package->sexp): Add optional repo argument, and use it to determine
whether to attempt to construct a source using the MELPA recipe.
(elpa->guix-package): Pass repo to elpa-package->sexp.
Signed-off-by: Christopher Baines <mail@cbaines.net>
b129b43475