openpty: limits for name

[Thomas Klausner <wiz%NetBSD.org@localhost>]

A Linux man page I found for openpty says:

BUGS
       Nobody knows how much space should be reserved for name. So,
       calling openpty() or forkpty() with non-NULL name may not be secure.

Our man page is silent on that.

The code in libutil/pty.c just does:
 if (name)
    (void)strcpy(name, linep);

I wonder if we (can and) want to promise a limit in the man page, or
just add a comment like the one in the Linux man page.
 Thomas