Ignore "safe" flag differences when e2fsck compares superblocks

Ignore "safe" flag differences when e2fsck compares superblocks

Recent e2fsprogs (1.40.3 and higher) fsck compares primary superblock to
backups, and if things differ, it forces a full check.  However, the
kernel has a penchant for updating flags the first time a feature is
used - attributes, large files, etc.

This is a bad idea, and we should break the kernel of this habit,
especially for the ext4 feature flags.  But for now, let's make e2fsck
avoid forcing a full check and backup except when absolutely
necessary.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>