[9fans] kfscmd atime considered harmful

[Richard Miller <miller@hamnavoe.demon.co.uk>]

Using disk/kfscmd atime, which reduces disk activity by preventing the
updating of access times when files and directories are accessed for
reading, has an unfortunate side effect of making the effects of wstat
somewhat ephemeral:

term% ls -l d
--rw-r----- M 8 miller miller 0 Oct 10 10:31 d/one
--rw-r----- M 8 miller miller 0 Oct 10 10:31 d/two
term% disk/kfscmd atime
atimes will not be updated
term% chmod 666 d/one
term% mv d/two d/three
term% ls -l d
--rw-rw-rw- M 8 miller miller 0 Oct 10 10:31 d/one
--rw-r----- M 8 miller miller 0 Oct 10 10:31 d/three
term% du >/dev/null
term% ls -l d
--rw-r----- M 8 miller miller 0 Oct 10 10:31 d/one
--rw-r----- M 8 miller miller 0 Oct 10 10:31 d/two

I'll send a suggested fix to 9trouble@plan9.bell-labs.com

-- Richard