Allow opening buttonized URL with secondary browser in rcirc

* lisp/net/browse-url.el (browse-url-button-open-url): Add autoload
cookie.
* lisp/net/rcirc.el (rcirc-markup-urls): Use
`browse-url-button-open-url' instead of just `browse-url' in order to
be able to use the secondary browser by giving a prefix arg.

lisp/net/browse-url.el

@@ -1782,6 +1782,7 @@ external browser instead of the default one."
         (funcall browse-url-secondary-browser-function url)
       (browse-url url))))
 
+;;;###autoload
 (defun browse-url-button-open-url (url)
   "Open URL using `browse-url'.
 If `current-prefix-arg' is non-nil, use

lisp/net/rcirc.el

@@ -2502,7 +2502,8 @@ If ARG is given, opens the URL in a new browser window."
 			'follow-link t
 			'rcirc-url url
 			'action (lambda (button)
-				  (browse-url (button-get button 'rcirc-url))))
+				  (browse-url-button-open-url
+                                   (button-get button 'rcirc-url))))
       ;; Record the URL if it is not already the latest stored URL.
       (unless (string= url (caar rcirc-urls))
         (push (cons url start) rcirc-urls)))))