Encode session information as unicode
    
    This will allow us to store any character for user information in
    any database.
    Postgres driver will automatically coerce for us, but some, like
    the sqlite backend, does not so this makes it work for both cases.
    
    Ticket: #213
    Signed-off-by: Patrick Uiterwijk <puiterwijk@redhat.com>
    Reviewed-by: Pierre-Yves Chibon <pingou@pingoured.fr>