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

Add -e to set arbitrary kernel environment variables.

Nextboot(8) can now set any combination of kernel name (-k), kernel
options (-o), and environment strings (-e). As a result of this change
-k also becomes optional.

Reviewed by: freebsd-current (Ian Lepore, pluknet@, jhb@)

Spelling fixes for sbin/

Uniformly refer to a file system as "file system".

Approved by: re

mdoc(7) police: overhaul.

Fix one misspelling and two punctuation nits.

Add a nextboot manual page.

Spotted by: brandt@fokus.gmd.de