How do I require ncurses >= 5.3 in LIB_DEPENDS?

[Matthias Andree]

I'm trying to make a port of the "cone" mail user agent (that supports
IMAP, SMAP, POP3, local Maildir, ..., gpg, spell checks) by Sam
Varshavchik.

My problem: How do I require ncurses >= 5.3 in LIB_DEPENDS?

Apparently FreeBSD 5's libncurses is current enough, but FreeBSD 4's
libnurses isn't up-to-date and some of the wide-character functions are
missing. How do I:

1. require the libncurses port in FreeBSD 4?
2. figure what is the oldest $OS_VERSION that shipped ncurses 5.3?

Thanks in advance,

-- 
Matthias Andree