Normalize percent escape sequence to upper case letters

* org-protocol.el (org-protocol-unhex-string): Normalize percent
escape sequence to upper case letters.

Otherwise the underlying function produces wrong results for percent
escape sequences that happen to use lower case characters.

lisp/org-protocol.el

@@ -313,7 +313,7 @@ encodeURIComponent. E.g. `%C3%B6' is the german Umlaut `ü'."
       (let* ((start (match-beginning 0))
 	     (end (match-end 0))
 	     (hex (match-string 0 str))
-	     (replacement (org-protocol-unhex-compound hex)))
+	     (replacement (org-protocol-unhex-compound (upcase hex))))
 	(setq tmp (concat tmp (substring str 0 start) replacement))
 	(setq str (substring str end))))
     (setq tmp (concat tmp str))