User-messaging is shaping up nicely.

I've so far limited this such that:

• Site-admins may send messages to any users.
• A user who receives a message may
  • Delete it.
  • Reply to it.

The net result is that ordinary users may not sent messages to each other. This will almost certainly change when I've worked on the code some more. But right now it works for the kind of "admin" operations I wish to make.

Plus it means I can get by with less testing - although the site test suite has been updated to cover the new code.