Bump USE_BDB requirement from yes to 42+, as nvi breaks with DB 4.1
probably due to BDB issue #8852, "Remove restriction that DB_TRUNCATE is
not allowed on files with subdatabases. This restriction was introduced
in 4.1.25." -- source: Berkeley DB 4.2.52 ChangeLog

nvi-devel works with db42 and db51 on 8.2-amd64.

Approved by: johans (maintainer)