Documentation request - Module requires PHP BCMATH extension

Hi

Great module, thanks! However I spent hours yesterday debugging to figure out that it requires BCMATH which i didn't have installed on the server. Actually the code that calls this is in Drupal's _openid_dh_binary_to_long in openid.inc, but still I think a mention in the readme file would have saved me a lot of time.

By the way, if you don't have BCMATH you get no error, and everything appears to work except when you get redirected back to your RP after accepting, the RP says something like "server denied check_authentication". In fact everything seems to work but no "assoc_handle" is generated by the OP and thus the session is not valid.

Thanks
Andy