MFC r335921:

Allow jail names (not just IDs) to be specified for: cpuset(1), ipfw(8),
sockstat(1), ugidfw(8)
These are the last of the jail-aware userland utilities that didn't work
with names.

PR: 229266
Differential Revision: D16047

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

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

Build usr.bin/ with WARNS=6 by default.

Also add some missing $FreeBSD$ to keep svn happy.

- Remove the -i argument when running a command to simplify things a
little bit and to prevent users from specifying a private mask that may
later restrict other group changes.
- Add a man page which brueffer generously contributed to.

Sponsored by: Nokia

Add a simple utility for manipulating cpusets. Man page will be available
soon.
- Lists of cpus may be specified with -l with ranges specified as low-high and
commas between individual cpus and ranges. ie -l 0-2,4,6-8.
- cpuset can modified -p pids, -t tids, or -s cpusetids.
- cpuset can -g get the current mask for any of the above.

Sponsored by: Nokia