More powerful recipe tests in preparation for refactorings

* slime-tests.el (slime-test-recipe-test-for): Simplify and make
more powerful.
(slime-test-recipe-check-repl): Removed it
(readme-recipe-autoload-on-lisp-visit): Adapt to new
`slime-test-recipe-test-for'. More readable.
(readme-recipe, traditional-recipe): Idem.