Find a prettier fix for loading pages before getting actor

[joepio]

I'm working on authentication #108 and noticed an annoyance. When I refresh the page, the first request will be sent as PublicAgent (no agent), and will therefore return a 401 if the resource requires signing in. However, the user will be signed in automatically a fraction later. This would result in the user being signed in, yet staring at an unauthorized page. He could press the retry button, of course, but that's suboptimal...

So I added some logic in the useResource hook, which keeps track of the current agent. If the agent changes, re-try fetching the resource. It works pretty well, but it adds quite a bit of logic, and possibly makes performance worse.

I'd like to find a better solution to this.

[joepio]

I currently went for re-fetching all unauthorized resources in the store when setAgent() is called with some Agent.