Please review: [Bug 531642] EntryUSN: RFE: a configuration option to make entryusn "global"

[Noriko Hosoi]

https://bugzilla.redhat.com/show_bug.cgi?id=531642

https://bugzilla.redhat.com/attachment.cgi?id=441366&action=diff
https://bugzilla.redhat.com/attachment.cgi?id=441366&action=edit

Fix description:
1. Introduced a config parameter nsslapd-entryusn-global: on|off to
    enable | disable the global mode.  By default, off.
    In the global mode, search on root dse returns "lastusn:<num>"
    without the backend subtype (e.g., "lastusn;userroot:<num>")
2. Added slapi_get_next_suffix_ext to mapping_tree.c, which visits
    children as well as siblings in the mapping tree.
    (Note: slapi_get_next_suffix does just siblings.)
3. import (ldif2db) adds "entryusn: 0" to every entry unless the
    entry already contains the entryusn attribute.
4. ldbm_back_delete, ldbm_back_modify, ldbm_back_modrdn: set
    ldap_result_code to pblock so that bepost plugin could see if
    the operation was successful or not.

See also http://directory.fedoraproject.org/wiki/Entry_USN#Global_mode

Thanks,
--noriko