Fixed theming.
#172170: Added OpenID integration.

#310906: Fixed authenticated user permission. Users who did not have permission to log in with Secure Site would get an error message, but could simply reload the page to log in.

#310906: More logic improvements. Added support for multiple authentication methods to be tried sequentially. Made digest authentication placeholder match SASL utilities more closely.

Set up digest authentication to use a placeholder function, _securesite_digest_manage(), until we can get an external program to handle passwords.

This is a first draft. Code will need to be simplified. Also, no attempt has been made to store user passwords securely.

Simplified 403 error handling.