Review and changes from Jocelyn Fiat

I would suggest to use a nonce manager object.
And it could be a reusable interface in the library.
Maybe using a deferred interface, and a in memory manager effective descendant for simple use, this way, user can decide to use a better descendant using database for instance, so that even if you restart the server or if you have multiple instance of the server (using FCGI for instance), then it will keep working.
For now, the current solution has severe limitation ... single user connection, and single server (and probably in a single thread). So these are point to think about.