Unbreak compilation-note-related tests

New sophisticated in-buffer navigation of compilation notes. Perhaps
too sophisticated...

* sly-tests.el (compile-defun)
(compile-defun-with-reader-conditionals): Restore `sly-previous-note'
call and make slightly more readable.

* sly.el (sly-next-note): New variable.
(sly--note-buttons-at, sly--search-note): New functions.
(sly-next-note, sly-previous-note, sly-goto-first-note): Unbreak
them.
(sly--add-in-buffer-note): Simplify: in-buffer notes are not
merged.
(sly--compilation-note-group-button): Must return the string for
Emacs 24.3
* swank.asd (defsystem :swank): order matters in lib/lisp/

Also in /lisp/backend