Mark all forum topics read

Users need the capability to mark all forum topics read. The attached patch does that for all forum topics and topics within a tid (if the user is browsing a sub-forum).

Two caveats:

1. a SELECT query, inserted into the FROM of the INSERT used to rebuild the {history} table, breaks Postgres but works fine in MySQL;
2. The patch in #481288: Add support for INSERT INTO ... SELECT FROM ... is required for this to work;