library: reverting tmpfs subtraction from cached (18-FEB-2014)

library: reverting tmpfs subtraction from cached (18-FEB-2014)

The subtraction was marked as reinforcing the misconception,
that memory in the page cache can be considered free.
The Cached value is not a sum of page cache and tmpfs,
as the tmpfs memory lives in the page cache and therefore
it's an inseparable part of it.