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

Ticket: http://www.rudder-project.org/redmine/issues/5575

To be merged in master
OK!

btw, the MD5 sums of both files match:
```
a94ea755ab695bc04f82b94d2e24a1ef  db_5.1.29.orig.tar.gz
a94ea755ab695bc04f82b94d2e24a1ef  db-5.1.29.tar.gz
```
so they are the same, no problems due to slightly different tarball to fear!