MMAPv1 should have a singleton RecordAccessTracker, rather than creating one per database

The RecordAccessTracker allocates a large table in which it stores accessed addresses, in order to keep track of what data is likely in physical memory. In 2.6 versions, this table was global to the process. 2.8.0-rc2 creates a table per database, which can have a large memory footprint in the case that many databases are open on the server. Instead, MMAPv1 should keep a singleton RecordAccessTracker.