* lib/rake.rb (FileUtils#rake_system): no longer needs workaround
on Windows. [ruby-core:21339]
* lib/rake/win32.rb (Rake::Win32#rake_system): ditto.
* lib/rake/win32.rb (Rake::Win32#win32_system_dir): no longer
needs environment variables other than APPDATA now.
* lib/rake.rb (Rake::Application#standard_system_dir): uses
platfrom specific definition on Windows system.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_1@21879 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
