Services API extension - Nbackup Support

From docs/README.services_extension.

Services API extension - Nbackup support.
(Alex Peshkov, peshkoff@mail.ru, 2008)

Nbackup performs two logical groups of operations - locking and unlocking a database and backup and restoring it. It doesn't make much sense duplicating locking and unlocking in using services, because that functionality is present remotely in via the SQL language interface (ALTER DATABASE). But backup and restore must be run on localhost and the only way to access them is via nbackup utility.

Therefore expanding the services API to support this functionalty is useful.

The following actions were added:

isc_action_svc_nbak - incremental nbackup,
isc_action_svc_nrest - incremental database restore.

The following parameters were added:
isc_spb_nbk_level - backup level (integer),
isc_spb_nbk_file - backup file name (string),
isc_spb_nbk_no_triggers - do not run DB triggers (option).

Samples of use of new parameters in fbsvcmgr utility (supposing login and
password have been set using some other method):

 Create backup level 0:
  fbsvcmgr service_mgr action_nbak dbname employee nbk_file e.nb0 nbk_level 0
 Create backup level 1:
  fbsvcmgr service_mgr action_nbak dbname employee nbk_file e.nb1 nbk_level 1
 Restore database from this files:
  fbsvcmgr service_mgr action_nrest dbname e.fdb nbk_file e.nb0 nbk_file e.nb1