Fix autoload bug when visiting lisp files early.

* Makefile (SELECTOR, OPTIONS): Respect previous value.

* slime-autoloads.el (lisp-mode-hook): Add `slime-lisp-mode-hook'
to it.

* slime-tests.el (slime-test-recipe-test-for): More generic, takes
`test-forms' and `check-fn' args. Uncomment relevant parts.
(readme-recipe): Adapt to new `slime-test-recipe-test-for'.
(readme-recipe-autoload-on-lisp-visit): New test.

* doc/slime.texi (Git Incantations): Fix typo.