fix https://github.com/rails/rails/issues/2582 (with testcase)

actionpack/lib/sprockets/assets.rake

@@ -42,7 +42,7 @@ namespace :assets do
         end
       end
 
-      File.open("#{manifest_path}/manifest.yml", 'w') do |f|
+      File.open("#{manifest_path}/manifest.yml", 'wb') do |f|
         YAML.dump(manifest, f)
       end
     end

railties/test/application/rake_test.rb

+# coding:utf-8
 require "isolation/abstract_unit"
 
 module ApplicationTests
@@ -244,5 +245,20 @@ def test_scaffold_tests_pass_by_default
 
       assert_match(/7 tests, 10 assertions, 0 failures, 0 errors/, content)
     end
+
+    def test_assets_precompile_with_utf8_filename
+      add_to_config <<-RUBY
+        config.assets.precompile = [ /\.png$$/, /application.(css|js)$/ ]
+      RUBY
+
+      Dir.chdir(app_path) do
+        `cp app/assets/images/rails.png app/assets/images/レイルズ.png`
+        `rake assets:precompile`
+        open("public/assets/manifest.yml") do |f|
+          assert_match(/レイルズ.png/, f.read)
+        end
+      end
+    end
+
   end
-end
\ No newline at end of file
+end