Users following "new message" links in emails should see latest version of request page

[sebbacon]

Report from Ben:

A user just reported that a new message hadn't appeared on WhatDoTheyKnow, and I was able to reproduce the problem.
The request in question was http://www.whatdotheyknow.com/request/hollie_bentley_prosecution_how_w, and the
incoming message arrived at Tue Feb 28 10:47:57 UTC 2012. Not having signed into WhatDoTheyKnow yet today, I looked
at the page at 10:57, and found that the incoming message wasn't displayed yet. I signed in (through the admin interface's
"sign in as this user" mechanism), and reloaded the public request page, and then the new message was visible. I signed
out, and reloaded the page again, and the new message remained visible.

Users generally look at request pages shortly after receiving emails about them, so it would be good if any caches could be
flushed when a new response to a request is received, or something like that.

The quick solution here is to use a cache-busting URL in the alerts emails. The better solution is to invalidate the cache when a new incoming message arrives.

[RichardTaylor]

We had this problem again today.

An authority responded to a request; the response could be seen by logged in admins (and presumably others who were logged in), but not the authority browsing the site.

[sebbacon]

Commit d6a5e30 should have fixed this issue (though note it depends on setting up Varnish correctly to handle cache invalidations)

[RichardTaylor]

We are still getting occasional emails from users saying when they click on alert / notification emails the message they have been notified about isn't shown.

I'm writing this as the WhatDoTheyKnow just got such an email from a user.

I've not personally caught a situation early enough to verify the problem still exists, but users are reporting it; albeit not at a level which suggests its a major issue.

[RichardTaylor]

We've not had a report of this issue for a while, but we've just had one on WhatDoTheyKnow:

I was requested to view the [...] response, when I went onto your website , there was no message to read.

~45 minutes later, on review by an administrator the response was visible.