Add -u (unbuffered output) after GNU sed.

Obtained from:	NetBSD
MFC after:	1 week
Fix a bug in bsdgrep(1) where patterns are not correctly
detected.

Certain criteria must be met for this bug to show up:

 * the -w flag is specified, and
 * neither -o or --color are specified, and
 * the pattern is part of another word in the line, and
 * the other word that contains the pattern occurs first

PR:		181973
MFC after:	3 days
Sponsored by:	The FreeBSD Foundation