(maybe_recoverable): Treat OVERWRITE_OLD_DIRS like DEFAULT_OLD_FILES.

[chaz/tar] / TODO

From: Roesinger Eric <ROESINGE@tce.com>
Date: Sat, 28 Jul 2001 18:43:43 -0500

It would be useful to be able to use '--remove-files' with '--diff',
to remove all files that compare successfully, when verifying a backup.