import: cpan: Propagate imported dependencies.

This is most often the need for perl module dependencies.

* guix/import/cpan.scm (cpan-module->sexp): 'inputs -> 'propagated-inputs.
* tests/cpan.scm ("cpan->guix-package"): Adjust accordingly.

guix/import/cpan.scm

@@ -242,7 +242,7 @@ META."
                        ;; have not yet had a need for cross-compiled perl
                        ;; modules, however, so we leave it out.
                        (convert-inputs '("configure" "build" "test")))
-       ,@(maybe-inputs 'inputs
+       ,@(maybe-inputs 'propagated-inputs
                        (convert-inputs '("runtime")))
        (home-page ,(string-append "http://search.cpan.org/dist/" name))
        (synopsis ,(assoc-ref meta "abstract"))

tests/cpan.scm

@@ -94,7 +94,7 @@
                                ('base32
                                 (? string? hash)))))
                    ('build-system 'perl-build-system)
-                   ('inputs
+                   ('propagated-inputs
                     ('quasiquote
                      (("perl-test-script" ('unquote 'perl-test-script)))))
                    ('home-page "http://search.cpan.org/dist/Foo-Bar")