reiserfs: add support for mount count incrementing

The following patch adds the fields for tracking mount counts and last
fsck timestamps to the superblock.  It also increments the mount count
on every read-write mount.

Reiserfsprogs 3.6.21 added support for these fields.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>