Bcmod() function breaks validation when not compiled in PHP.

Sometimes BC Math isn't compiled with PHP and then the function bcmod() breaks the validation. You can easily check if the function exists and when the function doesn't exist, use an alternate function.

You can read more on this page: http://nl1.php.net/manual/en/function.bcmod.php or this page: https://github.com/jschaedl/Iban/issues/17.

The alternate function works the same and doesn't break the validation.