Ref T4103. Ref T10078. This puts a user cache in front of notification and message counts.

This reduces the number of queries issued on every page by 4 (2x building the menu, 2x building Quicksand data).

Also fixes some minor issues:

• Daemons could choke on sending mail in the user's translation.
• No-op object updates could fail in the daemons.
• Questionable data access pattern in the file query coming out of the profile file cache.

• Sent myself notifications. Saw count go up.
• Cleared them by visiting objects and clearing all notifications. Saw count go down.
• Sent myself messages. Saw count go up.
• Cleared them by visiting threads. Saw count go down.