org-odt.el: Protect label references against downstream expansion

* contrib/lisp/org-odt.el
(org-export-odt-preprocess-label-references): Mark label as
protected text and protect it from being expanded downstream.

Fixes bug reported by Myles English here:
http://lists.gnu.org/archive/html/emacs-orgmode/2011-11/msg00069.html

contrib/lisp/org-odt.el

@@ -2209,7 +2209,8 @@ using `org-open-file'."
 	   ;; time we would have seen and collected all the label
 	   ;; definitions in `org-odt-entity-labels-alist'.
 	   (org-odt-format-tags
-	    "<text:sequence-ref text:ref-name=\"%s\"/>" "" label)) t t)))))
+	    "<text:sequence-ref text:ref-name=\"%s\"/>" ""
+	    (org-add-props label '(org-protected t)))) t t)))))
 
 ;; process latex fragments as part of
 ;; `org-export-preprocess-after-blockquote-hook'. Note that this hook