* lisp/files.el
(dir-locals--all-files): New &optional 'base-el-only' argument.
(dir-locals--base-file): New function.
(dir-locals-find-file): 'locate-dominating-file' only for the base
.dir-locals.el.
* test/lisp/files-tests.el
(files-test-dir-locals-2-solo): New test.
* test/lisp/files-resources/dir-locals-2-solo: New test support.
(files-test-dir-locals-2-paired): New test.
* test/lisp/files-resources/dir-locals-and-2: New test support.
* etc/NEWS (mode): Fall back on outline-mode in older Emacsen.
* lisp/files.el (hack-local-variables--find-variables): Use the
final mode: line (which is the same as having several mode: bits
in the header line.
* doc/emacs/dired.texi (Misc Dired Features): Document it (bug#23812).
* lisp/dired.el (dired-free-space): New user option.
(dired-insert-directory): Use it from here.
(dired--insert-disk-space): New function that uses the user option.
* lisp/files.el (insert-directory): Don't transform "total" here.
* lisp/ls-lisp.el (ls-lisp--insert-directory): Or here. Instead
just leave the "total <num>" bit alone, and let Dired transform it.
* test/lisp/files-tests.el (files-tests): Move "available" tests
to dired-tests.
* test/lisp/dired-tests.el (data-dir): Moved here.
* test/lisp/files-tests.el: Add 'insert-directory' tests.
* test/lisp/files-resources/insert-directory/: Create directories and files to
use for testing 'insert-directory'.
Add tests for 'insert-directory' base functionality and regression tests for
the issue where free space was reported for the current directory instead of
the target of 'list-directory' (Bug#50630).