[PATCH] md: add information about superblock version to /proc/mdstat

Leave it unchanged if the original (0.90) is used, incase it might be a
compatability problem.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>