(ITS#8859) Support backends without a database

[ondra@openldap.org]

Full_Name: Ondrej Kuznik
Version: master
OS: 
URL: https://github.com/mistotebe/openldap/tree/ITS8859
Submission from: (NULL) (82.10.24.68)


In order to support the load balancer within the slapd process and integrate
correctly, we declare it to be a backend as that is the best match - allows us
to register all the callbacks that a subsystem like this needs. The only problem
is that slapd will skip startup for backends that are not used by at least one
database.

The linked patch deals with this limitation and a few bugs encountered along the
way (some code has not been exercised in a long time and has suffered from some
bitrot).

The support to provide backend global configuration was nominally present but
has never worked with cn=config. The first two patches deal with that. The last
patch introduces a new backend flag that indicates that it should be started up
even if there is no database using it.

IPR notice:

The linked files are derived from OpenLDAP Software. All of the modifications to
OpenLDAP Software represented in the following patches were developed Symas
corp. Symas corp. has not assigned rights and/or interest in this work to any
party. I, Ondrej Kuznik am authorized by Symas corp. to release this work under
the following terms.

Symas corp. hereby place the following modifications to OpenLDAP Software (and
only these modifications) into the public domain. Hence, these modifications may
be freely used and/or redistributed for any purpose with or without attribution
and/or other notice.