* Move FreeBSD/DragonflyBSD out of meminfo add kvm.
This gives us SwapUsed, and everything under one roof.
* Fix typos per review.
* Update to use newer API.
* Remove premature optimization per PR feedback.
The devstat API expects us to reuse one devinfo for many invocations of
devstat_getstats. In particular, it allocates and resizes memory
referenced by devinfo.
Querying the number of devices separately from the device list itself is
racy. Devices may be added or removed between the two calls; and removed
devices would lead to a segfault.
Derek Marcotte