Issue 1106 - Add currentVersion Pref and compareVersions API

lib/api.js

 /*
  * This file is part of Adblock Plus <http://adblockplus.org/>,
  * Copyright (C) 2006-2014 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 149 matching lines @@
     },
 
     forceUpdateCheck: function(eventName)
     {
       checkForUpdates(_triggerEvent.bind(null, eventName));
     },
 
     getHostFromUrl: function(url)
     {
       return extractHostFromURL(url);      
+    },
+
+    compareVersions: function(v1, v2)
+    {
+      return Services.vc.compare(v1, v2);
     }
   };
 })();