This PR makes database.DB transactable by wrapping a basestore.Store
rather than a dbutil.DB directly. This allows us to run db.Transact(), get
a new transaction, then call tx.Repos() or whatever to get a more specific
store. It also allows us to use transactions for small tasks that don't have a store
associated with them, such as GetFirstServiceVersion. This makes it now possible
to remove the dbconn.Global reference in that function, and migrate those tests
to use dbtest.NewDB() rather than dbtesting.SetupGlobalDB().
Example:
db:=database.NewDB(sqlDB)tx,_:=db.Transact(ctx)tx.Repos()// do something with repostx.Users()// do something with users in the same transaction
