org-store-link: Fix storing of links to headlines in indirect buffers

* org.el (org-store-link): Storing of links to headlines in indirect
buffers was broken.  Fix it.

TINYCHANGE
Summary:

> When org-store-link is invoked on a headline in indirect buffer (as in a
> capture buffer), hyperlink gets created to the file and NOT the
> headline. This is a bug.
>
> The attached patch fixes this.
>
> Setup:
>
> # ~/.emacs
>
> (defun my-conversation-id ()
>   (interactive)
>
>   (remove-hook 'org-capture-before-finalize-hook 'my-conversation-id)
>
>   (let ((org-link-to-org-use-id t))
>     (call-interactively 'org-store-link)
>     )
>   )
>
> # org-capture-templates
>
>  ("x" "Conversations" entry
>   (file+headline "~/conversation.org" "Conversations")
>   "%(progn (add-hook 'org-capture-before-finalize-hook 'my-conversation-id) \"\")** Note taken on %U\n   %?  " :prepend t :empty-lines 1)
>
> Steps for reproduction:
>
> Trigger org-capture for the above capture entry.
>
> Examine conversation.org before/after the patch is applied. Note the
> absence/presence of IDs for the captured entry.
>
> Check for the stored links using C-c C-l. Note the file/headline links.
>
> # file conversation.org before and after the patch
>
> * Conversations
>
> ** Note taken on [2010-08-23 Mon 04:33]
>    :PROPERTIES:
>    :ID:       7e1974a6-8fa1-43cf-bef3-2adf37d99130
>    :END:
>
> ** Note taken on [2010-08-23 Mon 04:32]
>
> # (org-insert-link) showing stored links before and after the patch
>
> file:~/conversation.org (file:~/conversation.org)
> id:7e1974a6-8fa1-43cf-bef3-2adf37d99130 (Note taken on [2010-08-23 Mon 04:33])
>

lisp/org.el

@@ -8300,13 +8300,14 @@ For file links, arg negates `org-context-in-file-links'."
  	(setq cpltxt (concat "file:" file)
  	      link (org-make-link cpltxt))))
 
-     ((and buffer-file-name (org-mode-p))
+     ((and (buffer-file-name (buffer-base-buffer)) (org-mode-p))
       (setq custom-id (ignore-errors (org-entry-get nil "CUSTOM_ID")))
       (cond
        ((org-in-regexp "<<\\(.*?\\)>>")
 	(setq cpltxt
 	      (concat "file:"
-		      (abbreviate-file-name buffer-file-name)
+		      (abbreviate-file-name
+		       (buffer-file-name (buffer-base-buffer)))
 		      "::" (match-string 1))
 	      link (org-make-link cpltxt)))
        ((and (featurep 'org-id)
@@ -8328,11 +8329,13 @@ For file links, arg negates `org-context-in-file-links'."
 		     (error
 		      ;; probably before first headline, link to file only
 		      (concat "file:"
-			      (abbreviate-file-name buffer-file-name))))))
+			      (abbreviate-file-name
+			       (buffer-file-name (buffer-base-buffer))))))))
        (t
 	;; Just link to current headline
 	(setq cpltxt (concat "file:"
-			     (abbreviate-file-name buffer-file-name)))
+			     (abbreviate-file-name
+			      (buffer-file-name (buffer-base-buffer)))))
 	;; Add a context search string
 	(when (org-xor org-context-in-file-links arg)
 	  (setq txt (cond