Merge r266206 from head (by bjk):

  Review pass through jail.8

  Replace usage of "prison" with "jail", since that term has mostly dropped
  out of use.  Note once at the beginning that the "prison" term is equivalent,
  but do not use it otherwise. [1]

  Some grammar issues.

  Some mdoc formatting fixes.

  Consistently use \(em for em dashes, with spaces around it.

  Avoid contractions.

  Prefer ssh to telnet.

PR:		176832 [1]