-Fixed bug in session system (it would have occurred if we had ever had a session renewed after becoming too old, but before getting cleared by a collection cycle, and caused some odd behavior)
-Now compensating for Firefoxs' habit of not replacing older cookies. Instead of treating the `Cookie:` header as a single token value, we're treating it as a "; "-delimited list of token values. We use the first active token, or generate a new one and pass it down if none of them are still active.