Automatically call sudo in the install rake task.

Rakefile

@@ -113,7 +113,8 @@ END
   Rake::Task[:package].enhance { File.delete('REVISION') if File.exists?('REVISION') }
 
   task :install => [:package] do
-    sh %{gem install --no-ri pkg/haml-#{File.read('VERSION').strip}}
+    sudo = RUBY_PLATFORM =~ /win32/ ? 'sudo' : ''
+    sh %{#{sudo} gem install --no-ri pkg/haml-#{File.read('VERSION').strip}}
   end
 
   task :release => [:package] do