The halfwidth katakana code '\uff??' cannot be converted to the native code
on WindowsNT family. It can be reproducible on Windows 2000 and XP Pro Japanese
but not reproducible on Solaris.

Reproduction:
  - Obtain "unicode.txt" as attached.
  - Run native2ascii with -reverse option in ja locale.
    % native2ascii -reverse unicode.txt
    \uff71\uff72\uff73\uff74\uff75
    \uff76\uff77\uff78\uff79\uff7a
    \uff7b\uff7c\uff7d\uff7e\uff7f
    \uff80\uff81\uff82\uff83\uff84
    \uff85\uff86\uff87\uff88\uff89
    \uff8a\uff8b\uff8c\uff8d\uff8e
    \uff8f\uff90\uff91\uff92\uff93
    \uff94\uff95\uff96
    \uff9c\uff66\uff9d
    %

It should be converted properly on Windows.
Also, this works fine using 1.4.0 (Merlin) so this is a regression.