An update is due if the information has changed since the last update,
or if no update has been sent for 12 hours (to ensure that lost
updates are eventually replaced).

were last modified.

In future this will be used to determine when to send updates.

carry data.

Also changed the dispose() method of readers/writers/connections to
swallow any exceptions that occur, since the caller can't do anything
except log them.

transport subpackages.

accessed outside the lock.