Fix for double order creation

After the Spree::UsersController was modified to inherit from Spree::StoreController it inherited its before_filters including the set_current_order filter. The effect of this filter is to create an order in the database in certain conditions, in particular when there is no session[:order_id].

Once a user completes an order Spree clears the order_id session meaning that as soon as the user is redirected to the user#show page the set_current_order file creates a second order.

If you follow the logic of the set_current_order filter here you'll see what I mean:
https://github.com/spree/spree/blob/master/core/lib/spree/core/controller_helpers/order.rb

Seeing as the ability to run tests was down due to the issue with `undefined method `add_module' for Devise:Module` I haven't been able to run tests on the repository, although I can confirm it works within my website.