Japanese attachement filename is broken on Japanese Windows Ruby 1.9

<pre>
$ ruby --version
ruby 1.9.3p0 (2011-10-30) [i386-mingw32]
</pre>

h3. ChiliProject 2.6 Ruby 1.9.3

!chili-2.6.png!

h3. Redmine Rails 3.1.3 Ruby 1.9.3

!redmine-rails-3.1.3-ruby-1.9.3.png!