Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Update these scripts to be more userfriendly and usage safe.

Add fstab entries for ALTROOTSLICE and CFGSLICE, allowing us to do away with
most of the hardcoding of device names in installed convenience scripts.

Provide a new script (root/updatep) to easily update the ALTROOTSLICE. It
does the same as updatep1/updatep2 without hardcoded device names. If noone
protests, I'd like to get rid of updatep1/updatep2 at some point.

As an extra bonus: turn on the error led while updating (on hardware with a
led).

Add some runtime admin/tool scripts