Any backup & restore operation may be leaving opened files
if a file logger is being used. This implementes the close()
method, so every logger can close any resource.
Also, the recommended backup_controlled::destroy() method
now calls to new logger::destroy() method in charge of
deleting all the references and closing any resource.
Finally, some internally used controllers, were missing
their destroy call, leading to associated loggers to
remain open. Now all them are explicitly deltroyed.
When doing a backup or restore operation with the normal user interface,
if there is anything in the backup/restore log, it will now be displayed
at the end of the process below the Continue button.
If you have developer debugging enabled, it sets the display level to
LOG_DEBUG and there will always be content in the log. Otherwise, it
uses LOG_INFO which generally means the log is empty, and nothing
displays (no visible change for users).
