Update documentation of '.dir-locals-2.el'

See https://lists.gnu.org/r/emacs-devel/2017-11/msg00649.html
for more details.
* lisp/files.el (dir-locals-file-2): Remove unused constant.
* lisp/files.el (dir-locals-file): Mention ".dir-locals-2.el" in
the doc string.
* doc/lispref/variables.texi (Directory Local Variables): Mention
".dir-locals-2.el".
* etc/NEWS: Replace `dir-locals-file-2' mention with
`dir-locals-file'.

1 files changed, 6 insertions, 1 deletions

diff --git a/doc/lispref/variables.texi b/doc/lispref/variables.texi
index a871352b004..5bee0f9d82a 100644
--- a/doc/lispref/variables.texi
+++ b/doc/lispref/variables.texi
@@ -1919,7 +1919,12 @@ settings to any file in that directory or any of its subdirectories
 (optionally, you can exclude subdirectories; see below).
 If some of the subdirectories have their own @file{.dir-locals.el}
 files, Emacs uses the settings from the deepest file it finds starting
-from the file's directory and moving up the directory tree.  The file
+from the file's directory and moving up the directory tree.  This
+constant is also used to derive the name of a second dir-locals file
+@file{.dir-locals-2.el}.  If this second dir-locals file is present,
+then that is loaded instead of @file{.dir-locals.el}.  This is useful
+when @file{.dir-locals.el} is under version control in a shared
+repository and cannot be used for personal customizations.  The file
 specifies local variables as a specially formatted list; see
 @ref{Directory Variables, , Per-directory Local Variables, emacs, The
 GNU Emacs Manual}, for more details.