bug#15279: Info broken image

[Juri Linkov]

When Info can't find an image file it replaces the image
with the placeholder "[broken image]" even when there is
ASCII variant of the image.  It would be more user-friendly
to display ASCII variant if it is provided in the Info file.
Additionally this patch also displays the ALT attribute
in the tooltip like web browsers do.

=== modified file 'lisp/info.el'
--- lisp/info.el        2013-07-03 20:47:56 +0000
+++ lisp/info.el        2013-09-05 21:33:39 +0000
@@ -1611,11 +1611,15 @@ (defun Info-display-images-node ()
                                    ""))
                      (image (if (file-exists-p image-file)
                                 (create-image image-file)
-                              "[broken image]")))
+                              (or (cdr (assoc-string "text" parameter-alist))
+                                 (and src (concat "[broken image:" src "]"))
+                                 "[broken image]"))))
                 (if (not (get-text-property start 'display))
                     (add-text-properties
-                     start (point) `(display ,image rear-nonsticky 
(display)))))
+                     start (point)
+                    `(display ,image rear-nonsticky (display)
+                      help-echo ,(cdr (assoc-string "alt" parameter-alist))))))
             ;; text-only display, show alternative text if provided, or
             ;; otherwise a clue that there's meant to be a picture
             (delete-region start (point))