[PATCH] Allow to use procs when specifying defaults for routes

Hey,

with this patch it's possible to do something like this:

get ":locale/:book/pages/:page(/:version)" => "pages#show",
    :as => :page,
    :defaults => { :locale => Proc.new { I18n.locale }, :page => 1 }

page_path("catch-22", 5, 1) => "/en/catch-22/pages/5/1"
page_path("catch-22", :locale => :pl) => "/pl/catch-22/pages/1"

scope "/:locale", :defaults => { :locale => Proc.new { I18n.locale } } do
  resources :page
end

pages_path => "/en/pages"
pages_path(:locale => :pl) => "/pl/pages"

I couldn't figure out how to pass current controller instance or parameters to defaults block, but I guess it's going to be useful anyway.

I'm attaching a patch and a file that can be put i.e. into config/initializers to get this functionality without patching Rails.