Fixes #15 Issue with POP3/IMAP on Exchange 2010

Added methods to control the DISABLE_AUTHENTICATOR parameter used in the imap_open function
disableGssapiAuthenticator()
disableNtmlAuthenticator()
enableAuthentication()

Example of use:
    $server = new Server('example.com', '143');
    $server->disableGssapiAuthenticator();