In r292392 I modified the active queue scan to weigh clean pages
differently from dirty pages when attempting to meet the inactive queue
target. Specifically, I wanted clean pages to count more towards the
target, since they can be reclaimed with less work. Moreover, moving
more dirty pages to the laundry queue improves our ability to cluster
them when writing.
When r306706 was merged into the PQ_LAUNDRY branch, this mechanism was
broken. Fix it by scalaing the correct page shortage variable.