curs_overlay(3) on FreeBSD

The text 7edbddc33b34, as FreeBSD 2.1.7.1-RELEASE, FreeBSD 2.1.7-RELEASE, FreeBSD 2.1.5-RELEASE, FreeBSD 2.0.5-RELEASE shipped it.

overlay and manipulate overlapped ncurses windows

curs_overlay(3) on FreeBSD now