caches_action accepts store_options such as :expires_in

Then we will be able to do:

  class ProjectsController < ActionController::Base
    caches_action :show, :expires_in => 1.hour
  end

This is useful if you are using memcached.

Patch attached with tests included here:

http://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/416-caches_actions-accepts-cache_store-options-such-as-expires_in