(w32_load_system_font): Default charset to -1.

(w32_load_system_font): Default charset to -1.
(x_to_w32_charset): Match all fonts for unicode.
(w32_to_x_charset): New parameter; matching. Don't return partial or
wildcard charsets.
(w32_to_all_x_charsets): Don't return partial or wildcard charsets.
(w32_codepage_for_font): Return CP_UNICODE for unicode.
(w32_to_x_font): Match supplied charset to a real charset.
(enum_font_cb2): Always list unicode versions.