MFC 196392:

MFC 196392:

  Add support for backing up the old kernel when installing a new kernel
  using freebsd-update.  This applies to using freebsd-update in "upgrade
  mode" and normal freebsd-update on a security branch.

  The backup kernel will be written to /boot/kernel.old, if the directory
  does not exist, or the directory was created by freebsd-update in a
  previous backup.  Otherwise freebsd-update will generate a new directory
  name for use by the backup.  By default symbol files are not backed up
  to save diskspace and avoid filling up the root partition.

  This feature is fully configurable in the freebsd-update config file,
  but defaults to enabled.

  Reviewed by:	cperciva

Approved by:	re (kib)

git-svn-id: svn://svn.freebsd.org/base/stable/8@196393 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f