screen, ncurses and ncurses.mk

[Walter Schwarzenfeld]

The maintainer of sysutils/screen changed to USES=ncurses:base.

This will not work if ncurses:ports is installed (python uses it).

Ncurses.mk has:

if exists(${LOCALBASE}/lib/libncurses.so)

followed by a warning and exit.

So no port can install ncurses:base if ncurses:ports is installed.