(ITS#6801) New feature, add subtree-include support in meta backend

[jorge.perez.burgos@ericsson.com]

Full_Name: Jorge Perez Burgos
Version: 2.4.21
OS: linux
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (195.235.15.243)


I'd suggest to introduce a "subtree-include" directive, mutually exclusive with
"subtree-exclude", with different syntaxes, like:

"[dn[.<style>]:]<pattern>"

where <style> can be "subtree" or "regex" (other styles like "exact",
"onelevel", "subordinate" could make sense but would be of limited usefulness);
so, for example

"dn.subtree:<dn>" ("dn.subtree" implicit for backward compatibility)
"dn.regex:<pattern>" 

The "dn.<style>:" prefix is consistent with other features like ACLs, limits and
so.  There's ITS#5877 open about making this uniform across slapd for all
features.

Multiple patterns could be defined; the first that matches would stop execution.
 If configured as "subtree-exclude", a match would qualify the target as
"non-candidate" (current behavior for "subtree-exclude").  If configured as
"subtree-include", a match would qualify the target as "candidate".