* guix/scripts/build.scm: Use the right 'package-name->name+version'
procedure. Fixes a regression introduced in
1b846da8c3.
* tests/scripts-build.scm ("options->transformation, with-source, with
version"): New test.
* guix/scripts/build.scm (transform-package-source): Return a procedure
that expects a single object rather than a list of packages.
(options->transformation): Rewrite to precompute the list of applicable
transformations and to return a procedure that expects a single object
rather than a list of objects.
(options->derivations): Adjust accordingly.
* tests/scripts-build.scm: New file.
* Makefile.am (SCM_TESTS): Add it.