Combine these two functions into a single Verify function that is a member of WalletDatabase. Additionally, these are no longer static.
In order to override these later, the specific details of how the Read, Write, Erase, and Exists functions interact with the actual database file need to go into functions that are not templated.
Leave wallet/db.{cpp/h} for generic WalletDatabase stuff. The BDB specific stuff goes into bdb.{cpp/h}