Improve accessibility of enigma encryption options button in compose screen

plugins/enigma/enigma.js

@@ -58,6 +58,8 @@ window.rcmail && rcmail.addEventListener('init', function(evt) {
                 // don't close the menu on mouse click inside
                 e.stopPropagation();
             });
+
+            $('a.button.enigma').prop('tabindex', $('#messagetoolbar > a:first').prop('tabindex'));
         }
 
         $.each(['encrypt', 'sign'], function() {

plugins/enigma/lib/enigma_ui.php

@@ -761,7 +761,10 @@ class enigma_ui
             'label'    => 'encryption',
             'domain'   => $this->enigma->ID,
             'width'    => 32,
-            'height'   => 32
+            'height'   => 32,
+            'aria-owns'     => 'enigmamenu',
+            'aria-haspopup' => 'true',
+            'aria-expanded' => 'false',
             ), 'toolbar');
 
         $locks = (array) $this->rc->config->get('enigma_options_lock');

plugins/enigma/skins/larry/enigma.css

@@ -65,7 +65,9 @@ p.enigmaattachment a {
 /***** E-mail Compose Page *****/
 
 #messagetoolbar a.button.enigma {
-  background: url(enigma_icons.png) center -122px no-repeat;
+  background-image: url(enigma_icons.png);
+  background-position: center -122px;
+  background-repeat: no-repeat;
 }
 
 #enigmamenu {