LaTeX export: Use special formatting by link type interface

Patch by Christian Moe, who writes:

> It looks like support for formatting custom link types in LaTeX export
> is broken?
>
> I was trying to implement a custom link type with its own formatting
> function for HTML and LaTeX export, following the steps in
> org-bbdb.el.
>
> I've found that org-bbdb-export does not italicize bbdb links in
> LaTeX, nor does my own org-cite-export turn my custom =cite:= links
> into LaTeX =\cite{}= citations. Everything works fine in HTML export,
> but in LaTeX all custom link types get formatted as =\texttt{descr}=.
>
> I see that org-export-as-html and org-export-as-docbook look up
> org-link-protocols to get the function for formatting the link, but it
> seems that org-export-as-latex doesn't.
>
>

lisp/ChangeLog

@@ -1,5 +1,8 @@
 2010-05-12  Carsten Dominik  <carsten.dominik@gmail.com>
 
+	* org-latex.el (org-export-latex-links): Use the formatting
+	function of the link type, if it is available.
+
 	* org-table.el (org-table-get-remote-range): Return to
 	original buffer when retrieving remote reference.
 

lisp/org-latex.el

@@ -1822,7 +1822,7 @@ The conversion is made depending of STRING-BEFORE and STRING-AFTER."
 	    (attr (or (org-find-text-property-in-string 'org-attributes raw-path)
 		      (plist-get org-export-latex-options-plist :latex-image-options)))
 	    (label (org-find-text-property-in-string 'org-label raw-path))
-	    imgp radiop
+	    imgp radiop fnc
 	    ;; define the path of the link
 	    (path (cond
 		   ((member type '("coderef"))
@@ -1876,6 +1876,13 @@ The conversion is made depending of STRING-BEFORE and STRING-AFTER."
 		(setq path (org-export-latex-protect-amp path)
 		      desc (org-export-latex-protect-amp desc)))
 	      (insert (format org-export-latex-hyperref-format path desc)))
+
+	     ((functionp (setq fnc (nth 2 (assoc type org-link-protocols))))
+	      ;; The link protocol has a function for formatting the link
+	      (insert
+	       (save-match-data
+		 (funcall fnc (org-link-unescape raw-path) desc 'latex))))
+
 	     (t (insert "\\texttt{" desc "}")))))))