Avoid instance variable re-use trouble

This is the quickest/dumbest/safest way I could think of to prevent the instance variable reuse problems we have on dev.gitlab.org now.

config/routes.rb

@@ -30,7 +30,7 @@ Gitlab::Application.routes.draw do
end
# Enable Grack support
-  mount Grack::Auth.new({}), at: '/', constraints: lambda { |request| /[-\/\w\.]+\.git\//.match(request.path_info) }, via: [:get, :post]
+  mount Grack::AuthSpawner, at: '/', constraints: lambda { |request| /[-\/\w\.]+\.git\//.match(request.path_info) }, via: [:get, :post]
# Help
get 'help'                  => 'help#index'