File-Backup should not backup itself && watchdog-calls wrong in files_backup

When the backup target-location is part of the Drupal-directory (e.g. drupal/sites/default/backup), the backup-script backups all files - including the backups. This leads to fast growing backupfiles (e.g. 1GB, 2GB, 4GB, 8GB, etc).

For several reasons (e.g. Access to backups through normal Drupal-modules like filebrowser) backuping to a drupal-path seems logical to me. Nevertheless "backuping backups" is strange. The given patch excludes all files matching $dbname_files.tar.gz and $dbname_db.sql.

A warning: Setting /tmp as the default is very, very unsecure. In most cases we want a backup after e.g. a server failure occured - and in most cases, /tmp will be deleted on a regular schedule and/or with every restart.

While patching the tar-command, I found two additional errors:

1) exec($command,$output) creates $output as an array. Thus implode('
',$output) should be called to get the "line-wise" output of $command

2) Some calls to watchdog(..) are wrong.

The applied patch fixes all the above. To avoid the "exclude backup-files"-patch, simply remove the patch to $command. It would be better to add an option that allows to exclude backups.
It would be nice to integrate db_maintenance with backup-migrate (though both modules exclude each others backupfiles).