Unescape plain link before open

* org.el (org-open-at-point): Unescape plain link.

This should fix a problem with open plain links reported by
Sebastien Vauban.

lisp/org.el

@@ -9392,7 +9392,8 @@ application the system uses for this file type."
 	(save-excursion
 	  (when (or (org-in-regexp org-angle-link-re)
 		    (org-in-regexp org-plain-link-re))
-	    (setq type (match-string 1) path (match-string 2))
+	    (setq type (match-string 1)
+		  path (org-link-unescape (match-string 2)))
 	    (throw 'match t)))
 	(save-excursion
 	  (when (org-in-regexp (org-re "\\(:[[:alnum:]_@#%:]+\\):[ \t]*$"))