don't know exactly the reason, but here without this back-hdb suddenly starts crashings all times (since bdb_monitor_* stuff)

Note: the caller is expected to pass in a valid LDAP handle.  If not,
the assert will trigger to let him know his code is broken.

Note: need a way to close the connection too.

the entry to get nvals first, so the size can be computed.

(likely need to be applied to other backends)