Fixed PHP-1266: phpinfo() lists 'default' authentication mechanism

Also only list X509 if we have openssl support
Merge pull request #759 from bjori/PHP-1266-mech-list

Fixed PHP-1266: phpinfo() lists 'default' authentication mechanism

* bjori/PHP-1266-mech-list:
  Fixed PHP-1266: phpinfo() lists 'default' authentication mechanism