lower case external remote user - canonicalise email address
Make normalizing remote user e-mail optional (off by default).

I don't think we can make this change as is in case other institutions have configured their proxies to supply consistent e-mail addresses or other identifiers and these identifiers are not uniformly lower case. In such cases these changes (Pull Request 144) would break Galaxy's existing user management.
Document new normalize_remote_user_email option.