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

Ticket: http://www.rudder-project.org/redmine/issues/5575

To be merged in master
http://ftp.de.debian.org/debian/pool/main/d/db/db_5.1.29.orig.tar.gz comes from https://packages.debian.org/wheezy/libdb5.1 (the official Debian wheezy package) :)