e2fsck: improve error messages when the journal sb is corrupt

If the journal superblock is corrupt and the user declines to fix it
(or runs e2fsck -n), make sure the error messages are clear and
explain that e2fsck cannot (safely) proceed.

Addresses-Debian-Bug: #768162

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
4 files changed