add info about safe-local-variable to describe-variable

[Dan Nicolaescu]

AFAIK to find out whether a variable is safe or not one has to read
the source code. It would be nice to have describe-variable give this
information. 

Should I check this in? 
(suggestions for better wording/formating are welcome)

*** help-fns.el 18 Feb 2006 21:47:52 -0800      1.86
--- help-fns.el 28 Apr 2006 11:09:44 -0700      
***************
*** 630,635 ****
--- 630,636 ----
                               (indirect-variable variable)
                             (error variable)))
                     (obsolete (get variable 'byte-obsolete-variable))
+                  (safe-var (get variable 'safe-local-variable))
                     (doc (or (documentation-property variable 
'variable-documentation)
                              (documentation-property alias 
'variable-documentation))))
                (unless (eq alias variable)
***************
*** 641,646 ****
--- 642,656 ----
                  (princ (if (stringp (car obsolete)) (car obsolete)
                           (format "use `%s' instead." (car obsolete))))
                  (terpri))
+             
+             (when safe-var 
+               (princ "\nThis variable is safe to use as a file local 
variable")
+               (unless (eq safe-var t)
+                 (princ (format " only if its value\nsatisfies the predicate 
`%s'"
+                                safe-var)))
+               (princ ".")
+               (terpri))
+ 
              (princ "Documentation:\n")
                (princ (or doc "Not documented as a variable.")))
            ;; Make a link to customize if this variable can be customized.