Accessibility improvement, title for popup close button

Apparently it read as "times" in screen readers.

js/util.js

@@ -771,7 +771,7 @@ var SN = { // StatusNet
 
             form
                 .addClass('dialogbox')
-                .append('<button class="close">&#215;</button>')
+                .append('<button class="close" title="' + SN.msg('popup_close_button') + '">&#215;</button>')
                 .closest('.notice-options')
                     .addClass('opaque');
 

lib/action.php

@@ -460,6 +460,7 @@ class Action extends HTMLOutputter // lawsuit
 
             // TRANS: Localized tooltip for '...' expansion button on overlong remote messages.
             $messages['showmore_tooltip'] = _m('TOOLTIP', 'Show more');
+            $messages['popup_close_button'] = _m('TOOLTIP', 'Close popup');
 
             $messages = array_merge($messages, $this->getScriptMessages());