[PATCH] cfq-iosched.c: minor fixes

[PATCH] cfq-iosched.c: minor fixes

One critical fix and two minor fixes for 2.6.13-rc7:

- Max depth must currently be 2 to allow barriers to function on SCSI
- Prefer sync request over async in choosing the next request
- Never allow async request to preempt or disturb the "anticipation" for
  a single cfq process context. This is as-designed, the code right now
  is buggy in that area.

Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>