Use memcpy instead of strncpy when we know the length anyway. Modern gcc seems to think it knows how to detect misuse of strncpy, but it's wrong (in fact: very, very wrong) and the path of least resistance is to not try to fight with it.

Note when editing this in the source tree that the links to the help
text, mansupp, and the manual itself won't work - they're arranged so
they work after installation.