shuffles the timing and sleep calls in bgfsck from:
sleep timer_on io timer_off io io io io io io io
to
sleep io io io io io io io timer_on io timer_off
The original method basically guaranteed that the timed I/O included a
disk seek every time, which made bgfsck sleep for much longer than
necessary.
Submitted by: Dan Nelson
Reviewed by: kirk
08983aee40