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

The last big commit: let usr.sbin/ use WARNS=6 by default.

Add the new userland tool for manipulating extended attributes.

This will replace the existing getextattr(8) and setextattr(8) with
a single binary responding to the names getextattr, setextattr,
rmextattr and lsextattr.

This program is not yet connected to the build.

Sponsored by: DARPA and NAI Labs.