MFC r265249,r265250,r265251:

    - Add -J command/flag to filter by jail name/jid. This will automatically
      display the JID as well (the -j command/flag).
    - Add a hint for 'u' and 'J' command that '+' displays all.
    - Add J command to help.
MFC r251630:

  Bump the CPU/WCPU column width by one so that it fits values from 100% up to
  999.99% CPU.
MFC r265267:

  Fix width/alignment of JID column. Make it support up to the maximum 7-wide
  JIDs. On a system using jails for common tasks the JID can quickly increase.