From: Rick Lindsley <ricklind@us.ibm.com>

Fix bug #2230.

I've corresponded with the submitter and he did find a real bug -- when we
were merging I/O requests we didn't always take the oldest request start
time, which would cause a couple of the calculations like wait time and
average queue size to be too small.  He found it mathematically but having
done so, I think logic and inspection makes it easy to verify.