Replace "AccessControl::IsUserTheAdministrator" by equivalent logic

IsUserTheAdministrator is removed since AccessControl v1.0.5.0, so checking whether it is administrator account, I've used NameToSid and confirmed sid ends with "-500".

See http://support.microsoft.com/kb/243330 for list of sid account.
Merge pull request #5 from kenhys/replace-is-user-the-administrator

Replace "AccessControl::IsUserTheAdministrator" by equivalent logic