MFC r237581:

MFC r237581:
  Explicitly mention that setting the change and expiry times to zero is
  equivalent to leaving the time unset. [1]

  Wordsmith in the compat support section.

  Use a full path to nologin(8) in the context of setting it as a user's shell,
  keeping a separate cross-reference.

PR:		docs/169354 [1]
Approved by:	re (hrs), hrs (mentor)

git-svn-id: svn://svn.freebsd.org/base/stable/9@238162 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f