Log Message:
Back out last change related to moving ncurses/buildlink2.mk to
curses.buildlink2.mk.  This was wrong because we _really_ do want to
express that we want _n_curses when we include the buildlink2.mk file.

We should have a better way to say that the NetBSD curses doesn't
quite work well enough.  In fact, it's far better to depend on ncurses
by default, and exceptionally note when it's okay to use NetBSD curses
for specific packages.  We will look into this again in the future.