Link in registration request mail is broken

When using the "user regsitration" feature, sending a registration request builds a mail with a broken URL. Example:

http:/localhost:11111/nuxeo/site/userRegistration/validate/c6b07=
6ca-6ef7-48cc-8312-e22dd0349365

(notice the missing slash at http://)

It's handled correctly in most browsers/clients, but not with Zimbra, which disables the link.

I'll submit a patch shortly.