Add a .show_options super operation to reiserfs.

Use generic_show_options() and save the complete option string in
reiserfs_fill_super() and reiserfs_remount().
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>