capistrano pre-compile assets for rails 3.1

callbacks.rb

  desc "precompile the assets"
  task :precompile_assets, :roles => :web, :except => { :no_release => true } do
    run "cd #{current_path}; rm -rf public/assets/*"
    run "cd #{current_path}; RAILS_ENV=production bundle exec rake assets:precompile"
  end