curses: support linking against pdcurses
On Windows, ncurses are not available. Instead we link against PDCurses when building RubyInstaller.
Except that we required rename linking library to libcurses so curses extension finds it.
I would like to ask curses extension supports pdcurses linking library.
Attached is a patch that allows linking against unmodified pdcurses linking library.
I would like to port this change also to 1.9.3 in order to standardize building RubyInstaller.