MFC 219717,220363:

MFC 219717,220363:
- Add more details to the 'show battery' command including more raw
  capacity values, charge cycle count, temperature, and more detailed
  status.
- Add the ability to manage the state of write caching when the battery
  back-up is missing or dead.  The current state of this field is reported
  in 'mfiutil cache <volume>' and can be adjusted via
  'mfiutil cache <volume> bad-bbu-write-cache <enable|disable>'.  This
  setting should generally be disabled to avoid data loss.

git-svn-id: svn://svn.freebsd.org/base/stable/8@220665 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f