Give permanent-local property to per-buffer variables without defaults.

* doc/emacs/custom.texi (Examining): Update C-h v message.

* lisp/bindings.el: Assign a non-nil permanent-local property to
per-buffer variables which lack a default value.

* lisp/help-fns.el (describe-variable): In the "automatically becomes
local" notice, take note of permanent-local variables.

Fixes: debbugs:11930

doc/emacs/ChangeLog

 2012-07-13  Chong Yidong  <cyd@gnu.org>
 
+	* custom.texi (Examining): Update C-h v message.
+
 	* buffers.texi (Misc Buffer): Document view-read-only.
 
 2012-07-07  Chong Yidong  <cyd@gnu.org>

doc/emacs/custom.texi

@@ -766,7 +766,7 @@ displays something like this:
 fill-column is a variable defined in `C source code'.
 fill-column's value is 70
 
-Automatically becomes buffer-local when set in any fashion.
+Automatically becomes buffer-local when set.
 This variable is safe as a file local variable if its value
 satisfies the predicate `integerp'.
 

lisp/ChangeLog

+2012-07-13  Chong Yidong  <cyd@gnu.org>
+
+	* bindings.el: Assign a non-nil permanent-local property to
+	per-buffer variables which lack a default value (Bug#11930).
+
+	* help-fns.el (describe-variable): In the "automatically becomes
+	local" notice, take note of permanent-local variables.
+
 2012-07-13  Chong Yidong  <cyd@gnu.org>
 	* files.el (toggle-read-only): Doc fix and code cleanup.  New arg

lisp/bindings.el

@@ -650,9 +650,22 @@ okay.  See `mode-line-format'.")
         user-error ;; That's the main one!
         ))
 
-
 (make-variable-buffer-local 'indent-tabs-mode)
 
+;; These per-buffer variables are never reset by
+;; `kill-all-local-variables', because they have no default value.
+;; For consistency, we give them the `permanent-local' property, even
+;; though `kill-all-local-variables' does not actually consult it.
+
+(mapcar (lambda (sym) (put sym 'permanent-local t))
+	'(buffer-file-name default-directory buffer-backed-up
+	  buffer-saved-size buffer-auto-save-file-name
+	  buffer-read-only buffer-undo-list mark-active
+	  point-before-scroll buffer-file-truename
+	  buffer-file-format buffer-auto-save-file-format
+	  buffer-display-count buffer-display-time
+	  enable-multibyte-characters))
+
 ;; We have base64, md5 and sha1 functions built in now.
 (provide 'base64)
 (provide 'md5)

lisp/help-fns.el

@@ -852,7 +852,10 @@ it is displayed along with the global value."
                              (with-temp-buffer
                                (local-variable-if-set-p variable))))
                 (setq extra-line t)
-                (princ "  Automatically becomes buffer-local when set in any fashion.\n"))
+                (princ "  Automatically becomes ")
+		(if (get variable 'permanent-local)
+		    (princ "permanently "))
+		(princ "buffer-local when set.\n"))
 
               ;; Mention if it's an alias
               (unless (eq alias variable)