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

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

Per Regents of the University of Calfornia letter, remove advertising
clause.

# If I've done so improperly on a file, please let me know.

Use the correct function name as .Nm argument.

PR: 86169
Submitted by: Toby Peterson <toby@apple.com>
MFC after: 3 days

Add fgetwln(), a wide character version of fgetln().