Fixes #5575: Add an internal BDB version for slapd builds

Ticket: http://www.rudder-project.org/redmine/issues/5575

To be merged in master
I would rather we just use the link from oracle.com. Not that I don't trust Debian, it just makes it more complicated to trace source code. http://download.oracle.com/berkeley-db/db-5.1.29.tar.gz