MFC 222758, 222759, 222770:

MFC 222758, 222759, 222770:

- Document that when running 'su -m <user> -c <command>', <command> is
  run within a shell as <user>.
- Bump date
- Attempt to clear up some confusion in the following example, by
  stating the '-c' argument is passed to the shell, not to su(1), which
  would indicate the login class.

      'su -m <user> -c <command>'

PR:		157078

git-svn-id: svn://svn.freebsd.org/base/stable/8@222965 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f