curses KEY_* constants

[Bill Green]

I perhaps should have mentioned I linked the Python curses module against
ncurses rather than BSD curses.  Perhaps NetBSD's curses doesn't support this
feature, and that's why it's not included there. 

In any case, I removed the relevant #defines in _cursesmodule.c and got a
Python that includes all the KEY_ constants in the curses module, but these
constants (for the arrow keys at least) seem not to match the actual
keycodes.