Use OpenBSD's revamped description of strlcpy and strlcat.

This explanation is supposed to be simpler and better.  In particular
"comparing it to the snprintf API provides lots of value, since it raises the
bar on understanding, so that programmers/auditors will a better job calling
all 3 of these functions."

Requested by:	deraadt@cvs.openbsd.org
Obtained From:	OpenBSD
Reviewed by:	cperciva