ext3: make barrier options consistent with ext4

ext4 was updated to accept barrier/nobarrier mount options
in addition to the older barrier=0/1.  The barrier story
is complex enough, we should help people by making the options
the same at least, even if the defaults are different.

This patch allows the barrier/nobarrier mount options for ext3,
while keeping nobarrier the default.

It also unconditionally displays barrier status in show_options,
and prints a message at mount time if barriers are not enabled,
just as ext4 does.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>