I've added status option to send_file and x_send_file (rebased on current master)

Usage:

```ruby
app.config.middleware.insert_before(Rack::Lock, Rack::Rewrite) do
  maintenance_file = Rails.root.join('public', 'maintenance.html').to_s
  send_file /(.*)$(?<!css|png|jpg)/, maintenance_file, :status => 503, :if => Proc.new{|rack_env|
    File.exists?(maintenance_file)
  }
end
```